METHOD AND PRODUCT FOR REGULATING CELL RESPONSIVENESS TO EXTERNAL SIGNALS

Abstract: The present invention relates to isolated MEKK proteins, nucleic acid molecules having sequences that encode such proteins, and antibodies raised against such proteins. The present invention also includes methods to use such proteins to regulate signal transduction in a cell. The present invention also includes therapeutic compositions comprising such proteins or nucleic acid molecules that encode such proteins and their use to treat animals having medical disorders including cancer, inflammation, neurological disorders, autoimmune diseases, allergic reactions, and hormone-related diseases. When MEKK is expressed, it phosphorylates and activates MEKs including MEK-1, MEK-2 and JEK.

Description: METHOD AND PRODUCT FOR REGULATING CELL RESPONSIVENESS TO EXTERNAL SIGNALS FIELD OF THE INVENTION This invention relates to isolated nucleic acid molecules encoding MEKK proteins, substantially pure MEKK proteins, and products and methods for regulating signal transduction in a cell. SUMMARY OF THE INVENTION The present invention relates to a substantially pure MEKK protein capable of phosphorylating mammalian MEK protein, in which the MEKK protein comprises a catalytic domain. The present invention includes a substantially pure MEKK protein capable of regulating signals initiated from a growth factor receptor on the surface of a cell by regulating the activity of MAPK protein, the ability to regulate being divergent from Raf protein signal regulation. In particular, the substantially pure MEKK protein comprises at least a portion of an amino acid sequence encoded by a nucleic acid sequence that is capable of hybridizing under stringent conditions with a nucleic acid molecule encoding an amino acid sequence including SEQ ID N0:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID N0.10. The substantially pure MEKK protein capable of regulating the activity of MAPK protein, said protein having an amino acid sequence distinct from Raf protein. The present invention also includes a formulation comprising at least one isolated protein having at least a portion of an amino acid sequence encoded by a nucleic acid sequence that is capable of hybridizing under stringent conditions with a nucleic acid molecule encoding an amino acid sequence including SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10. One aspect of the present invention includes an isolated nucleic acid molecule having a sequence encoding a protein capable of phosphorylating mammalian MEK independent of Raf protein and capable of regulating the activity of MAPK protein. In particular, the present invention includes an isolated nucleic acid molecule capable of hybridizing under stringent conditions with a nucleic acid sequence selected from the group consisting of SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and SEQ ID NO:9. Another aspect of the present invention includes a recombinant molecule, comprising a nucleic acid molecule capable of hybridizing under stringent conditions with a nucleic acid sequence including SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and SEQ ID NO:9, in which the nucleic acid molecule is operatively linked to an expression vector. Yet another aspect of the present invention is a recombinant cell transformed with a recombinant molecule, comprising a nucleic acid molecule operatively linked to an expression vector, the nucleic acid molecule comprising a nucleic acid sequence capable of hybridizing under stringent conditions with a nucleic acid sequence selected from the group consisting of SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and SEQ ID NO:9 (i.e., the nucleic acid sequence shown in Table 1, Table 2, Table 3, Table 4 and Table 5) . The present invention also includes a method for regulating the homeostasis of a cell comprising regulating the activity of an MEKK-dependent pathway relative to the activity of a Raf-dependent pathway in the cell. In particular, the method comprises regulating the apoptosis of the cell. Such a method is useful for the treatment of a medical disorder. In particular, the method is useful for inhibiting tumorigenesis and autoimmunity. According to the present invention, the method for treatment of a disease, comprises administering to a patient an effective amount of a therapeutic compound comprising at least one regulatory molecule including a molecule capable of decreasing the activity of a Raf- dependent pathway, a molecule capable of increasing the activity of an MEKK-dependent pathway, and combinations thereof, in which the effective amount comprises an amount which results in the depletion of harmful cells involved in the disease. Also included in the present invention is a therapeutic compound capable of regulating the activity of an MEKK-dependent pathway in a cell identified by a process, comprising: (a) contacting a cell with a putative regulatory molecule; and (b) determining the ability of the putative regulatory compound to regulate the activity of an MEKK-dependent pathway in the cell by measuring the activation of at least one member of said MEKK-dependent pathway. One embodiment of the present invention includes a substantially pure protein, in which the protein is isolated using an antibody capable of selectively binding to an MEKK protein capable of phosphorylating mammalian MEK protein and capable of regulating the activity of MAPK protein independent of Raf protein, the antibody capable of being produced by a method comprising: (a) administering to an animal an effective amount of a substantially pure MEKK protein of the present invention; and (b) recovering an antibody capable of selectively binding to the MEKK protein. Another embodiment of the present invention includes an isolated antibody capable of selectively binding to an MEKK protein, the antibody capable of being produced by a method comprising administering to an animal an effective amount of a substantially pure protein of the present invention, and recovering an antibody capable of selectively binding to the MEKK protein. BACKGROUND OF THE INVENTION Mitogen-activated protein kinase (MAPKs) (also called extracellular signal-regulated kinases or ERKs) are rapidly activated in response to ligand binding by both growth factor receptors that are tyrosine kinases (such as the epidermal growth factor (EGF) receptor) and receptors that are coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) such as the thrombin receptor. The MAPKs appear to integrate multiple intracellular signals transmitted by various second messengers. MAPKs phosphorylate and regulate the activity of enzymes and transcription factors including the EGF receptor, Rsk 90, phospholipase Km, c-Myc, c-Jun and Elk-1/TCF. Although the rapid activation of MAPKs by receptors that are tyrosine kinases is dependent on Ras, G protein-mediated activation of MAPK appears to occur through pathways dependent and independent of Ras. Complementation analysis of the pheromone-induced signaling pathway in yeast has defined a protein kinase system that controls the activity of Spkl and Fus3-Kssl, the Sch±zosaccharomyces pombe and Saccharomyces cerevxsiae homologs of MAPK (see for example, B.R. Cairns et al., Genes and Dev. 6, 1305 (1992); B.J. Stevenson et al., Genes and Dev. 6, 1293 (1992); S.A. Nadin-Davis et al., EMBO J. 7, 985 (1988); Y. Wang et al., Mol . Cell . Biol . 11, 3554 (1991) . In S . cerevxsiae , the protein kinase Ste7 is the upstream regulator of Fus3-Kssl activity; the protein kinase Stell regulates Ste7. The S . pombe gene products Byrl and Byr2 are homologous to Ste7 and Stell, respectively. The MEK (MAPK Kinase or ERK Kinase) or MKK (MAP Kinase kinase) enzymes are similar in sequence to Ste7 and Byrl. The MEKs phosphorylate MAPKs on both tyrosine and threonine residues which results in activation of MAPK. The mammalian serine-threonine protein kinase Raf phosphorylates and activates MEK, which leads to activation of MAPK. Raf is activated in response to growth factor receptor tyrosine kinase activity and therefore Raf may activate MAPK in response to stimulation of membrane- associated tyrosine kinases. Raf is unrelated in sequence to Stell and Byr2. Thus, Raf may represent a divergence in mammalian cells from the pheromone-responsive protein kinase system defined in yeast. Cell and receptor specific differences in the regulation of MAPKs suggest that other Raf independent regulators of mammalian MEKs exist. Certain biological functions, such as growth and differentiation, are tightly regulated by signal transduction pathways within cells. Signal transduction pathways maintain the balanced steady state functioning of a cell. Disease states can arise when signal transduction in a cell breaks down, thereby removing the tight control that typically exists over cellular functions. For example, tumors develop when regulation of cell growth is disrupted enabling a clone of cells to expand indefinitely. Because signal transduction networks regulate a multitude of cellular functions depending upon the cell type, a wide variety of diseases can result from abnormalities in such networks. Devastating diseases such as cancer, autoimmune diseases, allergic reactions, inflammation, neurological disorders and hormone-related diseases can result from abnormal signal transduction. Despite a long-felt need to understand and discover methods for regulating cells involved in various disease states, the complexity of signal transduction pathways has precluded the development of products and processes for regulating cellular function by manipulating signal transduction pathways in a cell. As such, there remains a need for products and processes that permit the implementation of predictable controls of signal transduction in cells, thus enabling the treatment of various diseases that are caused by abnormal cellular function. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a schematic representation of the signal pathways of vertebrates and yeast. Fig. 2 is a schematic representation of the dual MEKK and Raf pathways divergent from Ras protein pathway. Fig. 3A shows a Northern (RNA) blot of a single 7.8 kb MEKK mRNA in several cell lines and mouse tissues. Fig. 3B shows a Southern (DNA) blot of the MEKK gene. Fig. 3C shows an immunoblot showing expression of the 78 kD and 50 kD forms of MEKK in rodent cell lines. Fig. 4 shows immunprecipitates of MEKK protein using MEKK antiserum. Fig. 5 shows immunoblotting of MEKK protein in immunoprecipitates and cell lysates. Fig. 6A shows the activation of MAPK in COS cells transfected with MEKK. Fig. 6B is an immunoblot showing expression of MEKK in cells either treated or not treated with EGF. Fig. 7 shows the activation and phosphorylation of MEK in COS cells transfected with MEKK. Fig. 8A shows the phosphorylation of MEK-1 by MEKK. Fig. 8B shows the time course of phosphorylation of MEK-1 by MEKK expressed in COS cells. Fig. 8C is an immunoblot of MEKK overexpressed in COS cells. Fig. 9A shows the phosphorylation of MAPK by activated MEK-1. Fig. 9B shows phosphorylation of MEK-1 by immunoprecipitated MEKK. Fig. 10A shows the phosphorylation of MEK-1 by activated Raf. Fig. 10B shows the phosphorylation state of Raf isolated from COS cells which are overexpressing MEKK and have been treated with EGF. Fig. 11 shows the relative ability of immunoprecipitated MEKK and Raf-B to phosphorylate kinase inactive MEK-1. Fig. 12 shows a time course of EGF-stimulated MEKK and Raf-B activation. Fig. 13 shows that the immunodepletion of Raf-B from MEKK immunoprecipitates has no effect on MEKK activity. Fig. 14 shows that the immunodepletion of Raf-B from MEKK immunoprecipitates decreases Raf-B activity. Fig. 15 shows MEKK activity in FPLC Mono Q ion- exchange column fractions of PC12 cell lysates. Fig. 16 shows inhibition of MEKK and Raf-B activation by dominant negative N 17 RAS expression. Fig. 17 shows activation of MEK protein by 98 kD MEKK. Fig. 18 shows inhibition of EGF activation of MEKK by forskolin. Fig. 19 shows improved MEKK activity by truncated MEKK molecules. Fig. 20 shows JNK activation by MEKK protein. Fig. 21 shows regulation of c-Myc controlled transcription and not CREB controlled transcription by MEKK protein. Fig. 22 is a schematic representation of MEKK regulation of c-Myc controlled transcription. Fig. 23 shows induction of p38 MAPK phosphorylation by MEKK 3. Fig. 24 shows induction of cellular apoptosis in Swiss 3T3 and REF52 cells by beauvericin. Fig. 25 shows induction of cellular apoptosis in REF52 cells by MEKK. Fig. 26 shows induction of cellular apoptosis in Swiss 3T3 and REF52 cells by MEKK. Fig. 27 shows 3 representative microscopic views of apoptotic REF52 cells expressing MEKK protein. Fig. 28 shows 3 representative microscopic views of apoptotic Swiss 3T3 cells expressing MEKK protein. Fig. 29 shows similar stimulation of MAPK activity by MEKK protein and Raf protein. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel mitogen ERK kinase kinase protein (MEKK) capable of regulating signal transduction in cells. The present invention includes a novel method for treating disease by regulating the activity of cells involved in such disease. The present invention is particularly advantageous in that the novel product and method of the present invention is capable of regulating a signal transduction pathway that can lead to cellular apoptosis. One embodiment of the present invention is an isolated MEKK protein. According to the present invention, an isolated protein is a protein that has been removed from its natural milieu. An isolated MEKK protein can, for example, be obtained from its natural source, be produced using recombinant DNA technology, or be synthesized chemically. As used herein, an isolated MEKK protein can be a full-length MEKK protein or any homologue of such a protein, such as an MEKK protein in which amino acids have been deleted (e.g. , a truncated version of the protein, such as a peptide) , inserted, inverted, substituted and/or derivatized (e.g., by glycosylation, phosphorylation, acetylation, myristoylation, prenylation, palmitoylation, amidation and/or addition of glycosylphosphatidyl inositol) , wherein the modified protein is capable of phosphorylating mitogen ERK kinase (MEK) and/or Jun ERK kinase (JEK) . A homologue of an MEKK protein is a protein having an amino acid sequence that is sufficiently similar to a natural MEKK protein amino acid sequence that a nucleic acid sequence encoding the homologue is capable of hybridizing under stringent conditions to (i.e., with) a nucleic acid sequence encoding the natural MEKK protein amino acid sequence. As used herein, stringent hybridization conditions refer to standard hybridization conditions under which nucleic acid molecules, including oligonucleotides, are used to identify similar nucleic acid molecules. Such standard conditions are disclosed, for example, in Sambrook et al.. Molecular Cloning: A Laboratory Manual , Cold Spring Harbor Labs Press, 1989. A homologue of an MEKK protein also includes a protein having an amino acid sequence that is sufficiently cross-reactive such that the homologue has the ability to elicit an immune response against at least one epitope of a naturally- occurring MEKK protein. The minimal size of a protein homologue of the present invention is a size sufficient to be encoded by a nucleic acid molecule capable of forming a stable hybrid with the complementary sequence of a nucleic acid molecule encoding the corresponding natural protein. As such, the size of the nucleic acid molecule encoding such a protein homologue is dependent on nucleic acid composition, percent homology between the nucleic acid molecule and complementary sequence, as well as upon hybridization conditions per se (e.g. , temperature, salt concentration, and formamide concentration) . The minimal size of such nucleic acid molecules is typically at least about 12 to about 15 nucleotides in length if the nucleic acid molecules are GC- rich and at least about 15 to about 17 bases in length if they are AT-rich. As such, the minimal size of a nucleic acid molecule used to encode an MEKK protein homologue of the present invention is from about 12 to about 18 nucleotides in length. There is no limit, other than a practical limit, on the maximal size of such a nucleic acid molecule in that the nucleic acid molecule can include a portion of a gene, an entire gene, or multiple genes, or portions thereof. Similarly, the minimal size of an MEKK protein homologue of the present invention is from about 4 to about 6 amino acids in length, with preferred sizes depending on whether a full-length, multivalent protein (i.e., fusion protein having more than one domain each of which has a function) , or a functional portion of such a protein is desired. MEKK protein homologues can be the result of allelic variation of a natural gene encoding an MEKK protein. A natural gene refers to the form of the gene found most often in nature. MEKK protein homologues can be produced using techniques known in the art including, but not limited to, direct modifications to a gene encoding a protein using, for example, classic or recombinant DNA techniques to effect random or targeted mutagenesis. The ability of an MEKK protein homologue to phosphorylate MEK and/or JEK protein can be tested using techniques known to those skilled in the art. Such techniques include phosphorylation assays described in detail in the Examples section. In one embodiment, an MEKK protein of the present invention is capable of regulating an MEKK-dependent pathway. According to the present invention, an MEKK- dependent pathway refers generally to a pathway in which MEKK protein regulates a pathway substantially independent of Raf, and a pathway in which MEKK protein regulation converges with common members of a pathway involving Raf protein, in particular, MEK protein (see Fig. 2) . A suitable MEKK-dependent pathway includes a pathway involving MEKK protein and JEK protein, but not Raf protein. One of skill in the art can determine that regulation of a pathway by an MEKK protein is substantially independent of Raf protein by comparing the ability of an MEKK protein and a Raf protein to regulate the phosphorylation of a downstream member of such pathway using, for example, the general method described in Example 16. An MEKK protein regulates a pathway substantially independently of Raf protein if the MEKK protein induces phosphorylation of a member of the pathway downstream of MEKK (e.g., proteins including JEK, JNK, Jun and/or ATF-2) by an amount significantly greater than that seen when Raf protein is utilized. For example, MEKK induction of phosphorylation of JNK is preferably at least about 10- fold, more preferably at least about 20-fold and even more preferably at least about 30-fold, greater phosphorylation of JNK protein than the phosphorylation induced when using Raf protein. If MEKK induction of phosphorylation is similar to Raf protein induction of phosphorylation, then one of skill in the art can conclude that regulation of a pathway by an MEKK protein includes members of a signal transduction pathway that could also include Raf protein. For example, MEKK induction of phosphorylation of MAPK is of a similar magnitude as induction of phosphorylation with Raf protein. A "Raf-dependent pathway" can refer to a signal transduction pathway in which Raf protein regulates a signal transduction pathway substantially independently of MEKK protein, and a pathway in which Raf protein regulation converges with common members of a pathway involving MEKK protein. The independence of regulation of a pathway by a Raf protein from regulation of a pathway by an MEKK protein can be determined using methods similar to those used to determine MEKK independence. In another embodiment, an MEKK protein is capable of regulating the activity of signal transduction proteins including, but not limited to, mitogen ERK kinase (MEK) , mitogen activated protein kinase (MAPK) , transcription control factor (TCF) , Ets-like-1 transcription factor (Elk- 1) , Jun ERK kinase (JEK) , Jun kinase (JNK) , stress activated MAPK proteins, Jun, activating transcription factor-2 (ATF-2) and/or Myc protein. As used herein, the "activity" of a protein can be directly correlated with the phosphorylation state of the protein and/or the ability of the protein to perform a particular function (e.g., phosphorylate another protein or regulate transcription) . Preferred MEK proteins regulated by an MEKK protein of the present invention include MEK-1 and/or MEK-2. Preferred MAPK proteins regulated by an MEKK protein of the present invention include p38 MAPK, p42 MAPK and/or p44 MAPK. A preferred MEKK protein that is capable of phosphorylating p38 MAPK protein includes a protein encoded by the nucleic acid sequence represented by SEQ ID NO:5 with a protein having the amino acid sequence represented by SEQ ID NO:7 being more preferred. Preferred stress activated MAPK proteins regulated by an MEKK protein of the present invention include Jun kinase (JNK) , stress activated MAPK-α and/or stress activated MAPK-β. An MEKK protein of the present invention is capable of increasing the activity of an MEK protein over basal levels of MEK (i.e., levels found in nature when not stimulated) . For example, an MEKK protein is preferably capable of increasing the phosphorylation of an MEK protein by at least about 2-fold, more preferably at least about 3-fold, and even more preferably at least about 4-fold over basal levels when measured under conditions described in Example 9. A preferred MEKK protein of the present invention is also capable of increasing the activity of an MAPK protein over basal levels of MAPK (i.e., levels found in nature when not stimulated) . For example, an MEKK protein of the present invention is preferably capable of increasing MAPK activity at least about 2-fold, more preferably at least about 3-fold, and even more preferably at least about 4- fold over basal activity when measured under the conditions described in Example 3. Moreover, an MEKK protein of the present invention is capable of increasing the activity of a JNK protein. JNK regulates the activity of the transcription factor JUN which is involved - in controlling the growth and differentiation of different cell types, such as T cells, neural cells or fibroblasts. JNK shows structural and regulatory homologies with MAPK. For example, an MEKK protein of the present invention is preferably capable of inducing the phosphorylation of JNK protein at least about 30 times more than Raf, more preferably at least about 40 times more than Raf, and even more preferably at least about 50 times more than Raf, when measured under conditions described in Example 16. A preferred MEKK protein of the present invention is additionally capable of inducing the phosphorylation of a c-Myc transcriptional transactivation domain protein in such a manner that the phosphorylated transcriptional transactivation domain of c-Myc is capable of regulating gene transcription. The ability of an MEKK protein to regulate phosphorylation of a c-Myc transcriptional transactivation domain protein exceeds the ability of Raf protein or cyclic AMP-dependent protein kinase to regulate a c-Myc protein. For example, an MEKK protein of the present invention is preferably capable of inducing luciferase gene transcription by phosphorylated c-Myc transcriptional transctivation domain protein at least about 25-fold, more preferably at least about 35-fold, and even more preferably at least about 45-fold, over Raf induction when measured under the conditions described in Example 17. Another aspect of the present invention relates to the ability of MEKK activity to be stimulated by growth factors including, but not limited to, epidermal growth factor (EGF) , neuronal growth factor (NGF) , tumor necrosis factor (TNF) , C5A, interleukin-8 (IL-8) , onocyte chemotactic protein 1 (MlPlα) , monocyte chemoattractant protein 1 (MCP- 1) , platelet activating factor (PAF) , N-Formyl-methionyl- leucyl-phenylalanine (FMLP) , leukotriene B 4 (LTB^R) , gastrin releasing peptide (GRP) , IgE, major histocompatibility protein (MHC) , peptide, superantigen, antigen, vasopressin, thrombin, bradykinin and acetylcholine. In addition, the activity of an MEKK protein of the present invention is capable of being stimulated by compounds including phorbol esters such as TPA. A preferred MEKK protein is also capable of being stimulated by EGF, NGF and TNF (especially TNFα) . Preferably, the activity of an MEKK protein of the present invention is capable of being stimulated at least 2-fold over basal levels (i.e., levels found in nature when not stimulated) , more preferably at least about 4-fold over basal levels and even more preferably at least about 6-fold over basal levels, when a cell producing the MEKK protein is contacted with EGF under the conditions described in Example 3. Similarly, the activity of an MEKK protein of the present invention is capable of being stimulated at least 1-fold over basal levels, more preferably at least about 2- fold over basal levels and even more preferably at least about 3-fold over basal levels by NGF stimulation, when a cell producing the MEKK protein is contacted with NGF under the conditions described in Example 9. Preferably, an MEKK protein of the present invention is capable of being stimulated at least 0.5-fold over basal levels, more preferably at least about 1-fold over basal levels and even more preferably at least about 2-fold over basal levels by TPA stimulation when a cell producing the MEKK protein is contacted with TPA under the conditions described in Example 9. TNF is capable of regulating cell death and other functions in different cell types. The present inventor discovered that MEKK stimulation by TNF is independent of Raf. Similarly, the present inventor is the first to appreciate that an MEKK protein can be directly stimulated by ultraviolet light (UV) damage of cells while a Raf- dependent pathway cannot. Therefore, both TNF and UV stimulate MEKK activity without substantially activating Raf. In addition, both UV and TNF activation of MEKK is Ras dependent. Another aspect of the present invention is the recognition that an MEKK protein of the present invention is capable of regulating the apoptosis of a cell, an ability not shared by Raf protein. As used herein, apoptosis refers to the form of cell death that comprises: progressive contraction of cell volume with the preservation of the integrity of cytoplasmic organelles; condensation of chromatin, as viewed by light or electron microscopy; and DNA cleavage, as determined by centrifuged sedimentation assays. Cell death occurs when the membrane integrity of the cell is lost and cell lysis occurs. Apoptosis differs from necrosis in which cells swell and eventually rupture. A preferred MEKK protein of the present invention is capable of inducing the apoptosis of cells, such that the cells have characteristics substantially similar to cytoplasmic shrinkage and/or nuclear condensation as shown in Figs. 24, 25, 26, 27 and 28. The apoptotic cells in Figs. 24 through 28 were obtained when cells were microinjected with expression plasmids encoding MEKK protein. Injected cells were identified using anti-β-Gal antibody and the DNA of the cells were stained with propidium iodide. Cytoplasmic organization was monitored using an anti-tubulin antibody. The cells were then imaged by differential fluorescent imaging microscopy using techniques standard in the art. The cells demonstrated apoptosis by displaying a morphology having cytoplasmic shrinkage and nuclear condensation. A schematic representation of the cell growth regulatory signal transduction pathway that is MEKK dependent is shown in Fig. 2. An MEKK protein of the present invention is capable of regulating the activity of JEK protein, JNK protein, Jun protein and/or ATF-2 protein, and Myc protein, such regulation being substantially, if not entirely, independent of Raf protein. Such Raf- independent regulation can regulate the growth characteristics of a cell, including the apoptosis of a cell. In addition, an MEKK protein of the present invention is capable of regulating the activity of MEK protein, which is also capable of being regulated by Raf protein. As such, an MEKK protein of the present invention is capable of regulating the activity of MAPK protein and members of the Ets family of transcription factors, such as TCF protein, also referred to as Elk-1 protein. Referring to Fig. 2, an MEKK protein of the present invention is capable of being activated by a variety of growth factors capable of activating Ras protein. In addition, an MEKK protein is capable of activating JNK protein which is also activated by Ras protein, but is not activated by Raf protein. As such, an MEKK protein of the present invention comprises a protein kinase at a divergence point in a signal transduction pathway initiated by different cell surface receptors. An MEKK protein is also capable of being regulated by TNF protein independent of Raf, thereby indicating an association of MEKK protein to a novel signal transduction pathway which is independent of Ras protein and Raf protein. Thus, an MEKK protein is capable of performing numerous unique functions independent of or by-passing Raf protein in one or more signal transduction pathways. An MEKK protein is capable of regulating the activity of MEK and/or JEK activity. As such, an MEKK protein is capable of regulating the activity of members of a signal transduction pathway that does not substantially include Raf activity. Such members include. but are not limited to, JNK, Jun, ATF and Myc protein. In addition, an MEKK protein is capable of regulating the members of a signal transduction pathway that does involve Raf, such members including, but are not limited to, MEK, MAPK and TCF. An MEKK protein of the present invention is thus capable of regulating the apoptosis of a cell independent of significant involvement by Raf protein. In addition to the numerous functional characteristics of an MEKK protein, an MEKK protein of the present invention comprises numerous unique structural characteristics. For example, in one embodiment, an MEKK protein of the present invention includes at least one of two different structural domains having particular functional characteristics. Such structural domains include an NH 2 -terminal regulatory domain that serves to regulate a second structural domain comprising a COOH- terminal protein kinase catalytic domain that is capable of phosphorylating an MEK protein and/or JEK protein. According to the present invention, an MEKK protein of the present invention includes a full-length MEKK protein, as well as at least a portion of an MEKK protein capable of performing at least one of the functions defined above. The phrase "at least a portion of an MEKK protein" refers to a portion of an MEKK protein encoded by a nucleic acid molecule that is capable of hybridizing, under stringent conditions, with a nucleic acid encoding a full-length MEKK protein of the present invention. Preferred portions of MEKK proteins are useful for regulating apoptosis in a cell. Additional preferred portions have activities useful for regulating MEKK kinase activity. Suitable sizes for portions of an MEKK protein of the present invention are as disclosed for MEKK protein homologues of the present invention. In another embodiment, an MEKK protein of the present invention includes at least a portion of an MEKK protein having molecular weights ranging from about 70 kD to about 250 kD as determined by Tris-glycine SDS-PAGE, preferably using an 8% polyacrylamide SDS gel (SDS-PAGE) and resolved using methods standard in the art. A preferred MEKK protein has a molecular weight ranging from about 75 kD to about 225 kD and even more preferably from about 80 kD to about 200 kD. In yet another embodiment, an MEKK protein of the present invention comprises at least a portion of an MEKK protein encoded by an mRNA (messenger ribonucleic acid) ranging from about 3.5 kb to about 12.0 kb, more preferably ranging from about 4.0 kb to about 11.0 kb, and even more preferably ranging from about 4.5 kb to about 10.0 kb. Particularly preferred MEKK proteins comprise at least a portion of an MEKK protein encoded by an mRNA having a size ranging from about 4.5 kb to about 5.0 kb, a size ranging from about 6.0 kb to about 6.5 kb, a size of about 7.0 kb, or a size ranging from about 8.0 kb to about 10.0 kb. In another embodiment, an NH 2 -terminal regulatory domain of the present invention includes an NH 2 -terminal comprising about 400 amino acids having at least about 10% serine and/or threonine residues, more preferably about 400 amino acids having at least about 15% serine and/or threonine residues, and even more preferably about 400 amino acids having at least about 20% serine and/or threonine residues. A preferred an NH 2 -terminal regulatory domain of the present invention includes an NH 2 -terminal comprising about 360 amino acids having at least about 10% serine and/or threonine residues, more preferably about 360 amino acids having at least about 15% serine and/or threonine residues, and even more preferably about 360 amino acids having at least about 20% serine and/or threonine residues. Another preferred an NH 2 -terminal regulatory domain of the present invention includes an NH 2 -terminal comprising about 370 amino acids having at least about 10% serine and/or threonine residues, more preferably about 370 amino acids having at least about 15% serine and/or threonine residues, and even more preferably about 370 amino acids having at least about 20% serine and/or threonine residues. In one embodiment, an MEKK protein of the present invention is devoid of SH2 and SH3 domains. In another embodiment, an MEKK protein of the present invention includes at least a portion of an MEKK protein homologue preferably having at least about 50%, more preferably at least about 75%, and even more preferably at least about 85% amino acid homology (identity within comparable regions) with the kinase catalytic domain of a naturally occurring MEKK protein. Another MEKK protein of the present invention also includes at least a portion of an MEKK homologue of the present invention has at least about 10%, more preferably at least about 20%, and even more preferably at least about 30% amino acid homology with the NH 2 -terminal regulatory domain of an MEKK protein of a naturally occurring MEKK protein. The sequences comprising the catalytic domain of an MEKK protein are involved in phosphotransferase activity, and therefore display a relatively conserved amino acid sequence. The NH 2 -terminal regulatory domain, of an MEKK protein, however, can be substantially divergent. The lack of significant homology between MEKK protein NH 2 -terminal regulatory domains is related to the regulation of each of such domains by different upstream regulatory proteins. For example, an MEKK protein can be regulated by the protein Ras, while others can be regulated independent of Ras. In addition, some MEKK proteins can be regulated by the growth factor TNFo, while others cannot. As such, the NH 2 -terminal regulatory domain of an MEKK protein provides selectivity for upstream signal transduction regulation, while the catalytic domain provides for MEKK substrate selectivity function. A preferred MEKK homologue has at least about 50%, more preferably at least about 75% and even more preferably at least about 85% amino acid homology with the kinase catalytic domain of an MEKK protein having an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 or SEQ ID NO:10. Another preferred MEKK homologue has at least about 10%, more preferably at least about 20% and even more preferably at least about 30% amino acid homology with the NH 2 -terminal regulatory domain of an MEKK protein having an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 or SEQ ID NO:10. In a preferred embodiment, an MEKK protein of the present invention includes at least a portion of an MEKK protein homologue of the present invention that is encoded by a nucleic acid molecule having at least about 50%, more preferably at least about 75%, and even more preferably at least about 85% homology with a nucleic acid molecule encoding the kinase catalytic domain of an MEKK protein. Another preferred MEKK protein homologue is encoded by a nucleic acid molecule having at least about 10%, more preferably at least about 20%, and even more preferably at least about 30% homology with a nucleic acid molecule encoding the NH 2 -terminal regulatory domain of an MEKK protein. Still another preferred MEKK homologue is encoded by a nucleic acid molecule having at least about 50%, more preferably at least about 75% and even more preferably at least about 85% amino acid homology with the kinase catalytic domain of an MEKK protein encoded by a nucleic acid sequence represented by SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 or SEQ ID NO:9. An MEKK homologue also includes those encoded by a nucleic acid molecule having at least about 10%, more preferably at least about 20% and even more preferably at least about 30% amino acid homology with the NH 2 -terminal regulatory domain of an MEKK protein encoded by a nucleic acid sequence represented by SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 or SEQ ID NO:9. An MEKK protein of the present invention, referred to here as MEKK 1, includes an MEKK protein having (i.e., including) at least a portion of the nucleic acid and/or an amino acid sequence shown in Table 1 and represented by SEQ ID N0:1 and SEQ ID NO:2, respectively. Table 1. TACACTCCTT GCCACAGTCT GGCAGAAAGA ATCAAACTTC AGAGACTCCT CCGGCCAGTT 60 GTAGACACTA TCCTTGTCAA GTGTGCAGAT CCAACAGCCG CACGAGTCAG CTGTCCATAT 120 CTACAGTGCT GGAACTCTGC AAGGGCCAAG CAGGAGAGCT GGCGGTTGGG AGAGAAATAC 180 TTAAAGCTGG GTCCATCGGG GTTGGTGGTG TCGATTACGT CTTAAGTTGT ATCCTTGGAA 240 ACCAAGCTGA ATCAAACAAC TGGCAAGAAC TGCTGGGTCG CCTCTGTCTT ATAGACAGGT 300 TGCTGTTGGA ATTTCCTGCT GAATTCTATC CTCATATTGT CAGTACTGAT GTCTCACΛAG 360 CTGAGCCTGT TGAAATCAGG TACAAGAAGC TGCTCTCCCT CTTAACCTTT GCCTTGCAAT 420 CCATTGACAA TTCCCACTCG ATGGTTGGCA AGCTCTCTCG GAGGATATAT CTGAGCTCTG 480 CCAGG ATG GTG ACC GCA GTG CCC GCT GTG TTT TCC AAG CTG GTA ACC 527 Met Val Thr Ala Val Pro Ala Val Phe Ser Lys Leu Val Thr 1 5 10 ATG CTT AAT GCT TCT GGC TCC ACC CAC TTC ACC AGG ATG CGC CGG CGT 575 Met Leu Asn Ala Ser Gly Ser Thr His Phe Thr Arg Met Arg Arg Arg 15 20 25 30 CTG ATG GCT ATC GCG GAT GAG GTA GAA ATT GCC GAG GTC ATC CAG CTG 623 Leu Met Ala He Ala Asp Glu Val Glu lie Ala Glu Val He Gin Leu 35 40 45 GGT GTG GAG GAC ACT GTG GAT GGG CAT CAG GAC AGC TTA CAG GCC GTG 671 Gly Val Glu Asp Thr Val Asp Gly His Gin Asp Ser Leu Gin Ala Val 50 55 60 GCC CCC ACC AGC TGT CTA GAA AAC AGC TCC CTT GAG CAC ACA GTC CAT 719 Ala Pro Thr Ser Cys Leu Glu Asn Ser Ser Leu Glu His Thr Val His 65 70 75 AGA GAG AAA ACT GGA AAA GGA CTA AGT GCT ACG AGA CTG AGT GCC AGC 767 Arg Glu Lys Thr Gly Lys Gly Leu Ser Ala Thr Arg Leu Ser Ala Ser 80 85 90 TCG GAG GAC ATT TCT GAC AGA CTG GCC GGC GTC TCT GTA GGA CTT CCC 815 Ser Glu Asp lie Ser Asp Arg Leu Ala Gly Val Ser Val Gly Leu Pro 95 100 105 110 AGC TCA ACA ACA ACA GAA CAA CCA AAG CCA GCG GTT CAA ACA AAA GGC 863 Ser Ser Thr Thr Thr Glu Gin Pro Lys Pro Ala Val Gin Thr Lys Gly 115 120 125 AGA CCC CAC AGT CAG TGT TTG AAC TCC TCC CCT TTG TCT CAT GCT CAA 911 Arg Pro His Ser Gin Cys Leu Asn Ser Ser Pro Leu Ser His Ala Gin 130 135 140 TTA ATG TTC CCA GCA CCA TCA GCC CCT TGT TCC TCT GCC CCG TCT GTC 959 Leu Met Phe Pro Ala Pro Ser Ala Pro Cys Ser Ser Ala Pro Ser Val 145 150 155 CCA GAT ATT TCT AAG CAC AGA CCC CAG GCA TTT GTT CCC TGC AAA ATA 1007 Pro Asp lie Ser Lys His Arg Pro Gin Ala Phe Val Pro Cys Lys He 160 165 170 CCT TCC GCA TCT CCT CAG ACA CAG CGC AAG TTC TCT CTA CAA TTC CAG 1055 Pro Ser Ala Ser Pro Gin Thr Gin Arg Lys Phe Ser Leu Gin Phe Gin 175 180 185 190 AGG AAC TGC TCT GAA CAC CGA GAC TCA GAC CAG CTC TCC CCA GTC TTC 1103 Arg Asn Cys Ser Glu His Arg Asp Ser Asp Gin Leu Ser Pro Val Phe 195 200 205 ACT CAG TCA AGA CCC CCA CCC TCC AGT AAC ATA CAC AGG CCA AAG CCA 1151 Thr Gin Ser Arg Pro Pro Pro Ser Ser Asn He His Arg Pro Lys Pro 210 215 220 TCC CGA CCC GTT CCG GGC AGT ACA AGC AAA CTA GGG GAC GCC ACA AAA 1199 Ser Arg Pro Val Pro Gly Ser Thr Ser Lys Leu Gly Asp Ala Thr Lys 225 230 235 AGT AGC ATG ACA CTT GAT CTG GGC AGT GCT TCC AGG TGT GAC GAC AGC 1247 Ser Ser Met Thr Leu Asp Leu Gly Ser Ala Ser Arg Cys Asp Asp Ser 240 245 250 TTT GGC GGC GGC GGC AAC AGT GGC AAC GCC GTC ATA CCC AGC GAC GAG 1295 Phe Gly Gly Gly Gly Asn Ser Gly Asn Ala Val He Pro Ser Asp Glu 255 260 265 270 ACA GTG TTC ACG CCG GTG GAG GAC AAG TGC AGG TTA GAT GTG AAC ACC 1343 Thr Val Phe Thr Pro Val Glu Asp Lys Cys Arg Leu Asp Val Asn Thr 275 280 285 GAG CTC AAC TCC AGC ATC GAG GAC CTT CTT GAA GCA TCC ATG CCT TCA 1391 Glu Leu Asn Ser Ser He Glu Asp Leu Leu Glu Ala Ser Met Pro Ser 290 295 300 AGT GAC ACG ACA GTC ACT TTC AAG TCC GAA GTC GCC GTC CTC TCT CCG 1439 Ser Asp Thr Thr Val Thr Phe Lys Ser Glu Val Ala Val Leu Ser Pro 305 310 315 GAA AAG GCC GAA AAT GAC GAC ACC TAC AAA GAC GAC GTC AAT CAT AAT 1487 Glu Lys Ala Glu Asn Asp Asp Thr Tyr Lys Asp Asp Val Asn His Asn 320 325 330 CAA AAG TGC AAA GAA AAG ATG GAA GCT GAA GAG GAG GAG GCT TTA GCG 1535 Gin Lys Cys Lys Glu Lys Met Glu Ala Glu Glu Glu Glu Ala Leu Ala 335 340 345 350 ATC GCC ATG GCG ATG TCA GCG TCT CAG GAT GCC CTC CCC ATC GTC CCT 1583 He Ala Met Ala Met Ser Ala Ser Gin Asp Ala Leu Pro He Val Pro 355 360 365 CAG CTG CAG GTG GAA AAT GGA GAA GAT ATT ATC ATC ATT CAG CAG GAC 1631 Gin Leu Gin Val Glu Asn Gly Glu Asp He He He He Gin Gin Asp 370 375 380 ACA CCA GAA ACT CTT CCA GGA CAT ACC AAA GCG AAA CAG CCT TAC AGA 1679 Thr Pro Glu Thr Leu Pro Gly His Thr Lys Ala Lys Gin Pro Tyr Arg 385 390 395 GAA GAC GCT GAG TGG CTG AAA GGC CAG CAG ATA GGC CTC GGA GCA TTT 1727 Glu Asp Ala Glu Trp Leu Lys Gly Gin Gin He Gly Leu Gly Ala Phe 400 405 410 TCT TCC TGT TAC CAA GCA CAG GAT GTG GGG ACT GGG ACT TTA ATG GCT 1775 Ser Ser Cys Tyr Gin Ala Gin Asp Val Gly Thr Gly Thr Leu Met Ala 415 420 425 430 GTG AAA CAG GTG ACG TAC GTC AGA AAC ACA TCC TCC GAG CAG GAG GAG 1823 Val Lys Gin Val Thr Tyr Val Arg Asn Thr Ser Ser Glu Gin Glu Glu 435 440 445 GTG GTG GAA GCG TTG AGG GAA GAG ATC CGG ATG ATG GGT CAC CTC AAC 1871 Val Val Glu Ala Leu Arg Glu Glu He Arg Met Met Gly His Leu Asn 450 455 460 CAT CCA AAC ATC ATC CGG ATG CTG GGG GCC ACG TGC GAG AAG AGC AAC 1919 His Pro Asn He He Arg Met Leu Gly Ala Thr Cys Glu Lys Ser Asn 465 470 475 TAC AAC CTC TTC ATT GAG TGG ATG GCG GGA GGA TCT GTG GCT CAC CTC 1967 Tyr Asn Leu Phe He Glu Trp Met Ala Gly Gly Ser Val Ala His Leu 480 485 490 TTG AGT AAA TAC GGA GCT TTC AAG GAG TCA GTC GTC ATT AAC TAC ACT 2015 Leu Ser Lys Tyr Gly Ala Phe Lys Glu Ser Val Val He Asn Tyr Thr 495 500 505 510 GAG CAG TTA CTG CGT GGC CTT TCC TAT CTC CAC GAG AAC CAG ATC ATT 2063 Glu Gin Leu Leu Arg Gly Leu Ser Tyr Leu His Glu Asn Gin He He 515 520 525 CAC AGA GAC GTC AAA GGT GCC AAC CTG CTC ATT GAC AGC ACC GGT CAG 2111 His Arg Asp Val Lys Gly Ala Asn Leu Leu He Asp Ser Thr Gly Gin 530 535 540 AGG CTG AGA ATT GCA GAC TTT GGA GCT GCT GCC AGG TTG GCA TCA AAA 2159 Arg Leu Arg He Ala Asp Phe Gly Ala Ala Ala Arg Leu Ala Ser Lys 545 550 555 GGA ACC GGT GCA GGA GAG TTC CAG GGA CAG TTA CTG GGG ACA ATT GCA 2207 Gly Thr Gly Ala Gly Glu Phe Gin Gly Gin Leu Leu Gly Thr He Ala 560 565 570 TTC ATG GCG CCT GAG GTC CTA AGA GGT CAG CAG TAT GGT AGG AGC TGT 2255 Phe Met Ala Pro Glu Val Leu Arg Gly Gin Gin Tyr Gly Arg Ser Cys 575 580 585 590 GAT GTA TGG AGT GTT GGC TGC GCC ATT ATA GAA ATG GCT TGT GCA AAA 2303 Asp Val Trp Ser Val Gly Cys Ala He He Glu Met Ala Cys Ala Lys 595 600 605 CCA CCT TGG AAT GCA GAA AAA CAC TCC AAT CAT CTC GCC TTG ATA TTT 2351 Pro Pro Trp Asn Ala Glu Lys His Ser Asn His Leu Ala Leu He Phe 610 615 620 AAG ATT GCT AGC GCA ACT ACT GCA CCG TCC ATC CCG TCA CAC CTG TCC 2399 Lys He Ala Ser Ala Thr Thr Ala Pro Ser He Pro Ser His Leu Ser 625 630 635 CCG GGT CTG CGC GAC GTG GCC GTG CGC TGC TTA GAA CTT CAG CCT CAG 2447 Pro Gly Leu Arg Asp Val Ala Val Arg Cys Leu Glu Leu Gin Pro Gin 640 645 650 GAC CGG CCT CCG TCC AGA GAG CTG CTG AAA CAT CCG GTC TTC CGT ACC 2495 Asp Arg Pro Pro Ser Arg Glu Leu Leu Lys His Pro Val Phe Arg Thr 655 660 665 670 ACG TGG TAGTTAATTG TTCAGATCAG CTCTAATGGA GACAGGATAT CGAACCGGGA 2551 Thr Trp GAGAGAAAAG AGAACTTGTG GGCGACCATG CCGCTAACCG CAGCCCTCAC GCCACTGAAC 2611 AGCCAGAAAC GGGGCCAGCG GGGAACCGTA CCTAAGCATG TGATTGACAA ATCATGACCT 2671 GTACCTAAGC TCGATATGCA GACATCTACA GCTCGTGCAG GAACTGCACA CCGTGCCTTT 2731 CACAGGACTG GCTCTGGGGG ACCAGGAAGG CGATGGAGTT TGCATGACTA AAGAACAGAA 2791 GCATAAATTT ATTTTTGGAG CACTTTTTCA GCTAATCAGT ATTACCATGT ACATCAACAT 2851 GCCCGCCACA TTTCAAACTC AGACTGTCCC AGATGTCAAG ATCCACTGTG TTTGAGTTTG 2911 TTTGCAGTTC CCTCAGCTTG CTGGTAATTG TGGTGTTTTG TTTTCGATGC AAATGTGATG 2971 TAATATTCTT ATTTTCTTTG GATCAAAGCT GGACTGAAAA TTGTACTGTG TAATTATTTT 3031 TGTGTTTTTA ATGTTATTTG GTACTCGAAT TGTAAATAAC GTCTACTGCT GTTTATTCCA 3091 GTTTCTACTA CCTCAGGTGT CCTATAGATT TTTCTTCTAC CAAAGTTCAC TCTCAGAATG 3151 AAATTCTACG TGCTGTGTGA CTATGACTCC TAAGACTTCC AGGGCTTAAG GGCTAACTCC 3211 TATTAGCACC TTACTATGTA AGCAAATGCT ACAAAAAAAA AAAAAAAAA 3260 An MEKK protein of the present invention, referred to here as MEKK 2, includes an MEKK protein having at least a portion of the nucleic acid and/or amino acid sequence shown in Table 2 and represented by SEQ ID NO:3 and SEQ ID NO:4, respectively. Table 2. GGTGGCGGCC GCTCTAGAAC TAGTGGATCC CCCGGGCTGC AGGAATTCGG CACGAGGGAC 60 GATCCAGCGG CAGAGTCGCC GCTTCCGCTT CGCTGCTTCT CCGGTCGGCG ACGCGGGCCC 120 GGGGCTTCCT TTTCATCGGC CCAGCTTATT CCGCGGGCCC CGGGGCTGCA GCTACCCAGA 180 AGCGGCGAAG AGGCCCTGGG CTGCGCGCCC GCTGTCCCAT GTGAAGCAGG TTGGGCCTGG 240 TCCCCGGCCC GTGCCCGGTT GTCTGCGGCC CTTCAGGCCT CAGGGACCCC CGCGAGGCGC 300 TGCTCCTGGG GGGCGCGGTG ACAGGCCGTG CGGGGGCGGA GGGGCCAGCT CGGTGGCCTC 360 CTCTCGGCCC TCGCGTCCGC GATCCCGCCC AGCGGCCGGG CAATAAAGAA TGTTGATGGG 420 AGAACCATTT TCCTAATTTT CAAATTATTG AGCTGGTCGC GCATA ATG GAT GAT 474 Met Asp Asp 1 CAG CAA GCT TTG AAT TCA ATC ATG CAA GAT TTG GCT GTC CTT CAT AAG 522 Gin Gin Ala Leu Asn Ser He Met Gin Asp Leu Ala Val Leu His Lys 5 10 15 CCA GTC GGC CAG CAT TAT CTT TAC AAG AAA CCA GGA AAG CAA AAC CTT 570 Pro Val Gly Gin His Tyr Leu Tyr Lys Lys Pro Gly Lys Gin Asn Leu 20 25 30 35 CAT CAC CAA AAA AAC AGA ATG ATG TTC GAG TCA AAT TTG AAC ATA GAG 618 His His Gin Lys Asn Arg Met Met Phe Glu Ser Asn Leu Asn He Glu 40 45 50 GAG GAA AAA AGG ATC CTG CAG GTT ACT AGA CCA GTT AAA CTA GAA GAC 666 Glu Glu Lys Arg He Leu Gin Val Thr Arg Pro Val Lys Leu Glu Asp 55 60 65 CTG AGA TCT AAG TCT AAG ATC GCC TTT GGG CAG TCT ATG GAT CTA CAC 714 Leu Arg Ser Lys Ser Lys He Ala Phe Gly Gin Ser Met Asp Leu His 70 75 80 TAT ACC AAC AAT GAG TTG GTA ATT CCG TTA ACT ACC CAA GAT GAC TTG 762 Tyr Thr Asn Asn Glu Leu Val He Pro Leu Thr Thr Gin Asp Asp Leu 85 90 95 GAC AAA GCT GTG GAA CTG CTG GAT CGC AGT ATT CAC ATG AAG AGT CTC 810 Asp Lys Ala Val Glu Leu Leu Asp Arg Ser He His Met Lys Ser Leu 100 105 110 115 AAG ATA TTA CTT GTA GTA AAT GGG AGT ACA CAG GCT ACT AAT TTA GAA 858 Lys He Leu Leu Val Val Asn Gly Ser Thr Gin Ala Thr Asn Leu Glu 120 125 130 CCA TCA CCG TCA CCA GAA GAT TTG AAT AAT ACA CCA CTT GGT GCA GAG 906 Pro Ser Pro Ser Pro Glu Asp Leu Asn Asn Thr Pro Leu Gly Ala Glu 135 140 145 AGG AAA AAG CGG CTA TCT GTA GTA GGT CCC CCT AAT AGG GAT AGA AGT 954 Arg Lys Lys Arg Leu Ser Val Val Gly Pro Pro Asn Arg Asp Arg Ser 150 155 160 TCC CCT CCT CCA GGA TAC ATT CCA GAC ATA CTA CAC CAG ATT GCC CGG 1002 Ser Pro Pro Pro Gly Tyr He Pro Asp He Leu His Gin He Ala Arg 165 170 175 AAT GGG TCA TTC ACT AGC ATC AAC AGT GAA GGA GAG TTC ATT CCA GAG 1050 Asn Gly Ser Phe Thr Ser He Asn Ser Glu Gly Glu Phe He Pro Glu 180 185 190 195 AGC ATG GAC CAA ATG CTG GAT CCA TTG TCT TTA AGC AGC CCT GAA AAT 1098 Ser Met Asp Gin Met Leu Asp Pro Leu Ser Leu Ser Ser Pro Glu Asn 200 205 210 TCT GGC TCA GGA AGC TGT CCG TCA CTT GAT AGT CCT TTG GAT GGA GAA 1146 Ser Gly Ser Gly Ser Cys Pro Ser Leu Asp Ser Pro Leu Asp Gly Glu 215 220 225 AGC TAC CCA AAA TCA CGG ATG CCT AGG GCA CAG AGC TAC CCA GAT AAT 1194 Ser Tyr Pro Lys Ser Arg Met Pro Arg Ala Gin Ser Tyr Pro Asp Asn 230 235 240 CAT CAG GAG TTT ACA GAC TAT GAT AAC CCC ATT TTT GAG AAA TTT GGA 1242 His Gin Glu Phe Thr Asp Tyr Asp Asn Pro He Phe Glu Lys Phe Gly 245 250 255 AAA GGA GGA ACA TAT CCA AGA AGG TAC CAC GTT TCC TAT CAT CAC CAG 1290 Lys Gly Gly Thr Tyr Pro Arg Arg Tyr His Val Ser Tyr His His Gin 260 265 270 275 GAG TAT AAT GAC GGT CGG AAG ACT TTT CCA AGA GCT AGA AGG ACC CAG 1338 Glu Tyr Asn Asp Gly Arg Lys Thr Phe Pro Arg Ala Arg Arg Thr Gin 280 285 290 GGC ACC AGT TTC CGG TCT CCT GTG AGC TTC AGT CCT ACT GAT CAC TCC 1386 Gly Thr Ser Phe Arg Ser Pro Val Ser Phe Ser Pro Thr Asp His Ser 295 300 305 TTA AGC ACT AGT AGT GGA AGC AGT GTC TTT ACC CCA GAG TAT GAC GAC 1434 Leu Ser Thr Ser Ser Gly Ser Ser Val Phe Thr Pro Glu Tyr Asp Asp 310 315 320 AGT CGA ATA AGA AGA CGG GGG AGT GAC ATA GAC AAT CCT ACT TTG ACT 1482 Ser Arg Ile Arg Arg Arg Gly Ser Asp Ile Asp Asn Pro Thr Leu Thr 325 330 335 GTC ACA GAC ATC AGC CCA CCC AGC CGT TCA CCT CGA GCT CCG ACC AAC 1530 Val Thr Asp He Ser Pro Pro Ser Arg Ser Pro Arg Ala Pro Thr Asn 340 345 350 355 TGG AGA CTG GGC AAG CTG CTT GGC CAA GGA GCT TTT GGT AGG GTC TAC 1578 Trp Arg Leu Gly Lys Leu Leu Gly Gin Gly Ala Phe Gly Arg Val Tyr 360 365 370 CTC TGC TAT GAT GTT GAT ACC GGA AGA GAG CTG GCT GTT AAG CAA GTT 1626 Leu Cys Tyr Asp Val Asp Thr Gly Arg Glu Leu Ala Val Lys Gin Val 375 380 385 CAG TTT AAC CCT GAG AGC CCA GAG ACC AGC AAG GAA GTA AAT GCA CTT 1674 Gin Phe Asn Pro Glu Ser Pro Glu Thr Ser Lys Glu Val Asn Ala Leu 390 395 400 GAG TGT GAA ATT CAG TTG TTG AAA AAC TTG TTG CAT GAG CGA ATT GTT 1722 Glu Cys Glu He Gin Leu Leu Lys Asn Leu Leu His Glu Arg He Val 405 410 415 CAG TAT TAT GGC TGT TTG AGG GAT CCT CAG GAG AAA ACA CTT TCC ATC 1770 Gin Tyr Tyr Gly Cys Leu Arg Asp Pro Gin Glu Lys Thr Leu Ser He 420 425 430 435 TTT ATG GAG CTC TCG CCA GGG GGT TCA ATT AAG GAC CAA CTA AAA GCC 1818 Phe Met Glu Leu Ser Pro Gly Gly Ser He Lys Asp Gin Leu Lys Ala 440 445 450 TAC GGA GCT CTT ACT GAG AAC GTG ACG AGG AAG TAC ACC CGT CAG ATT 1866 Tyr Gly Ala Leu Thr Glu Asn Val Thr Arg Lys Tyr Thr Arg Gin He 455 460 465 CTG GAG GGG GTC CAT TAT TTG CAT AGT AAT ATG ATT GTC CAT AGA GAT 1914 Leu Glu Gly Val His Tyr Leu His Ser Asn Met He Val His Arg Asp 470 475 480 ATC AAA GGA GCA AAT ATC TTA AGG GAT TCC ACA GGC AAT ATC AAG TTA 1962 He Lys Gly Ala Asn He Leu Arg Asp Ser Thr Gly Asn He Lys Leu 485 490 495 GGA GAC TTT GGG GCT AGT AAA CGG CTT CAG ACC ATC TGT CTC TCA GGC 2010 Gly Asp Phe Gly Ala Ser Lys Arg Leu Gin Thr He Cys Leu Ser Gly 500 505 510 515 ACA GGA ATG AAG TCT GTC ACA GGC ACG CCA TAC TGG ATG AGT CCT GAG 2058 Thr Gly Met Lys Ser Val Thr Gly Thr Pro Tyr Trp Met Ser Pro Glu 520 525 530 GTC ATC AGT GGA GAA GGC TAT GGA AGA AAA GCA GAC ATC TGG AGT GTA 2106 Val He Ser Gly Glu Gly Tyr Gly Arg Lys Ala Asp He Trp Ser Val 535 540 545 GCA TGT ACT GTG GTA GAA ATG CTA ACT GAA AAG CCA CCT TGG GCT GAA 2154 Ala Cys Thr Val Val Glu Met Leu Thr Glu Lys Pro Pro Trp Ala Glu 550 555 560 TTT GAA GCA ATG GCT GCC ATC TTT AAG ATC GCC ACT CAG CCA ACG AAC 2202 Phe Glu Ala Met Ala Ala He Phe Lys He Ala Thr Gin Pro Thr Asn 565 570 575 CCA AAG CTG CCA CCT CAT GTC TCA GAC TAT ACT CGG GAC TTC CTC AAA 2250 Pro Lys Leu Pro Pro His Val Ser Asp Tyr Thr Arg Asp Phe Leu Lys 580 585 590 595 CGG ATT TTT GTA GAG GCC AAA CTT CGA CCT TCA GCG GAG GAG CTC TTG 2298 Arg He Phe Val Glu Ala Lys Leu Arg Pro Ser Ala Glu Glu Leu Leu 600 605 610 CGG CAC ATG TTT GTG CAT TAT CAC TAGCAGCGGC GGCTTCGGTC CTCCACCAGC 2352 Arg His Met Phe Val His Tyr His 615 620 TCCATCCTCG CGGCCACCTT CTCTCTTACT GCACTTTCCT TTTTTATAAA AAAGAGAGAT 2412 GGGGAGAAAA AGACAAGAGG GAAAATATTT CTCTTGATTC TTGGTTAAAT TTGTTTAATA 2472 ATAATAGTAA ACTAAAAAAA AAAAAAAAAA A 2503 An MEKK protein of the present invention, referred to here as MEKK 3, includes an MEKK protein having at least a portion of the nucleic acid and/or amino acid sequence shown in Table 3 and represented by SEQ ID NO:5 and SEQ ID NO:6, respectively. Table 3. AGGGAACAAA AGCTGGAGCT CCACCGCGGT GGCGGCCGCT CTAGAACTAG TGGATCCCCC 60 GGGCTGCAGG AATTCGGCAC GAGGAACAGT GGCCGGTCGG AGCGTCTTCT GGACTTCAGG 120 ACTCGCAGGC GGCCCGGTCG AGTGGCGCCG CCGAGGCCGG GTTGGGCCGA GCCTGGGAGC 180 GCCGGGGATG TAGCGGGCCA ACCTGCTCAT GCCACAGCGC CCGGCCGCGG CCGAGCCGGA 240 GCCTGGGGAG GCGGCGGGGG CCCCGAGCGC AGCCCACGGC CCCCGCGCGG AGCCAGGCCC 300 GCTGCCGTCC CCGCCGCCCG CTCCCCCGGC ATGCAGCCCC GGCTGCGGAG GTGACACTTC 360 TGGGCTGTAG TCGCCACCGC CGCCTCCGCC ATCGCCACC ATG GAT GAA CAA GAG 414 Met Asp Glu Gin Glu 1 5 GCA TTA GAC TCG ATC ATG AAG GAC CTG GTG GCC CTC CAG ATG AGC CGA 462 Ala Leu Asp Ser He Met Lys Asp Leu Val Ala Leu Gin Met Ser Arg 10 15 20 CGA ACC CGG TTG TCT GGA TAT GAG ACC ATG AAG AAT AAG GAC ACA GGT 510 Arg Thr Arg Leu Ser Gly Tyr Glu Thr Met Lys Asn Lys Asp Thr Gly 25 30 35 CAC CCA AAC AGG CAG AGT GAC GTC AGA ATC AAG TTT GAA CAC AAT GGG 558 His Pro Asn Arg Gin Ser Asp Val Arg He Lys Phe Glu His Asn Gly 40 45 50 GAG AGA CGA ATT ATA GCA TTC AGC CGG CCT GTG AGA TAC GAA GAT GTG 606 Glu Arg Arg He He Ala Phe Ser Arg Pro Val Arg Tyr Glu Asp Val 55 60 65 GAG CAC AAG GTG ACA ACA GTC TTT GGG CAG CCT CTT GAT TTG CAT TAT 654 Glu His Lys Val Thr Thr Val Phe Gly Gin Pro Leu Asp Leu His Tyr 70 75 80 85 ATG AAT AAT GAG CTC TCC ATC CTG TTG AAA AAC CAA GAT GAT CTC GAT 702 Met Asn Asn Glu Leu Ser He Leu Leu Lys Asn Gin Asp Asp Leu Asp 90 95 100 AAA GCC ATT GAC ATT TTG GAT AGA AGC TCA AGT ATG AAA AGC CTT AGG 750 Lys Ala He Asp He Leu Asp Arg Ser Ser Ser Met Lys Ser Leu Arg 105 110 115 ATA CTA CTG TTA TCC CAA GAC AGA AAC CAT ACT AGT TCC TCT CCC CAC 798 He Leu Leu Leu Ser Gin Asp Arg Asn His Thr Ser Ser Ser Pro His 120 125 130 TCT GGA GTG TCC AGG CAG GTT CGG ATC AAG CCT TCC CAG TCT GCA GGG 846 Ser Gly Val Ser Arg Gin Val Arg He Lys Pro Ser Gin Ser Ala Gly 135 140 145 GAT ATA AAT ACC ATC TAC CAA GCT CCT GAG CCC AGA AGC AGG CAC CTG 894 Asp He Asn Thr He Tyr Gin Ala Pro Glu Pro Arg Ser Arg His Leu 150 155 160 165 TCT GTC AGC TCC CAG AAC CCT GGC CGA AGC TCT CCT CCC CCG GGA TAT 942 Ser Val Ser Ser Gin Asn Pro Gly Arg Ser Ser Pro Pro Pro Gly Tyr 170 175 180 GTA CCT GAG CGA CAA CAG CAC ATT GCC CGG CAA GGA TCC TAT ACG AGC 990 Val Pro Glu Arg Gin Gin His He Ala Arg Gin Gly Ser Tyr Thr Ser 185 190 195 ATC AAC AGC GAA GGT GAA TTC ATC CCA GAG ACC AGC GAA CAG TGT ATG 1038 He Asn Ser Glu Gly Glu Phe He Pro Glu Thr Ser Glu Gin Cys Met 200 205 210 CTA GAT CCC CTC AGC AGT GCC GAA AAT TCC TTG TCA GGA AGC TGC CAA 1086 Leu Asp Pro Leu Ser Ser Ala Glu Asn Ser Leu Ser Gly Ser Cys Gin 215 220 225 TCC TTG GAC AGG TCA GCA GAC AGC CCA TCC TTC AGG AAA TCA CAA ATG 1134 Ser Leu Asp Arg Ser Ala Asp Ser Pro Ser Phe Arg Lys Ser Gin Met 230 235 240 245 TCC CGA GCC CGG AGC TTC CCA GAC AAC AGA AAG GAA TGC TCA GAT CGG 1182 Ser Arg Ala Arg Ser Phe Pro Asp Asn Arg Lys Glu Cys Ser Asp Arg 250 255 260 GAG ACC CAG CTC TAT GAT AAA GGT GTC AAA GGT GGA ACC TAT CCC AGG 1230 Glu Thr Gin Leu Tyr Asp Lys Gly Val Lys Gly Gly Thr Tyr Pro Arg 265 270 275 CGC TAC CAT GTG TCT GTG CAT CAC AAA GAC TAC AAT GAT GGC AGA AGA 1278 Arg Tyr His Val Ser Val His His Lys Asp Tyr Asn Asp Gly Arg Arg 280 285 290 ACA TTT CCC CGA ATA CGA CGG CAT CAA GGC AAC CTA TTC ACT CTG GTG 1326 Thr Phe Pro Arg He Arg Arg His Gin Gly Asn Leu Phe Thr Leu Val 295 300 305 CCC TCA AGT CGC TCC TTG AGC ACA AAT GGC GAG AAC ATG GGT GTA GCT 1374 Pro Ser Ser Arg Ser Leu Ser Thr Asn Gly Glu Asn Met Gly Val Ala 310 315 320 325 GTG CAA TAC CTG GAC CCC CGT GGG CGC CTA CGG AGT GCA GAC AGT GAG 1422 Val Gin Tyr Leu Asp Pro Arg Gly Arg Leu Arg Ser Ala Asp Ser Glu 330 335 340 AAT GCC CTC ACT GTG CAG GAA AGG AAT GTG CCA ACC AAA TCT CCT AGT 1470 Asn Ala Leu Thr Val Gin Glu Arg Asn Val Pro Thr Lys Ser Pro Ser 345 350 355 GCT CCC ATC AAT TGG CGT CGG GGG AAG CTC CTG GGT CAA GGT GCC TTC 1518 Ala Pro He Asn Trp Arg Arg Gly Lys Leu Leu Gly Gin Gly Ala Phe 360 365 370 GGC AGG GTC TAC TTG TGC TAT GAT GTG GAC ACA GGA CGT GAA CTT GCT 1566 Gly Arg Val Tyr Leu Cys Tyr Asp Val Asp Thr Gly Arg Glu Leu Ala 375 380 385 TCT AAG CAG GTC CAG TTT GAC CCA GAT AGT CCT GAG ACA AGC AAG GAG 1614 Ser Lys Gin Val Gin Phe Asp Pro Asp Ser Pro Glu Thr Ser Lys Glu 390 395 400 405 GTG AGT GCT CTG GAG TGT GAG ATC CAG TTG CTG AAG AAC CTG CAG CAT 1662 Val Ser Ala Leu Glu Cys Glu He Gin Leu Leu Lys Asn Leu Gin His 410 415 420 GAG CGC ATT GTG CAG TAC TAC GGC TGC CTG CGG GAC CGT GCT GAG AAG 1710 Glu Arg He Val Gin Tyr Tyr Gly Cys Leu Arg Asp Arg Ala Glu Lys 425 430 435 ATC CTC ACC ATC TTT ATG GAG TAT ATG CCA GGG GGC TCT GTA AAA GAC 1758 He Leu Thr He Phe Met Glu Tyr Met Pro Gly Gly Ser Val Lys Asp 440 445 450 CAG TTG AAG GCC TAC GGA GCT CTG ACA GAG AGT GTG ACC CGC AAG TAC 1806 Gin Leu Lys Ala Tyr Gly Ala Leu Thr Glu Ser Val Thr Arg Lys Tyr 455 460 465 ACC CGG CAG ATT CTG GAG GGC ATG TCA TAC CTG CAC AGC AAC ATG ATT 1854 Thr Arg Gin He Leu Glu Gly Met Ser Tyr Leu His Ser Asn Met He 470 475 480 485 GTG CAT CGG GAC ATC AAG GGA GCC AAT ATC CTC CGA GAC TCA GCT GGG 1902 Val His Arg Asp He Lys Gly Ala Asn He Leu Arg Asp Ser Ala Gly 490 495 500 AAT GTG AAG CTT GGG GAT TTT GGG GCC AGC AAA CGC CTA CAG ACC ATC 1950 Asn Val Lys Leu Gly Asp Phe Gly Ala Ser Lys Arg Leu Gin Thr He 505 510 515 TGC ATG TCA GGG ACA GGC ATT CGC TCT GTC ACT GGC ACA CCC TAC TGG 1998 Cys Met Ser Gly Thr Gly He Arg Ser Val Thr Gly Thr Pro Tyr Trp 520 525 530 ATG AGT CCT GAA GTC ATC AGT GGC GAG GGC TAT GGA AGA AAG GCA GAC 2046 Met Ser Pro Glu Val He Ser Gly Glu Gly Tyr Gly Arg Lys Ala Asp 535 540 545 GTG TGG AGC CTG GGC TGT ACT GTG GTG GAA ATG CTG ACA GAG AAA CCA 2094 Val Trp Ser Leu Gly Cys Thr Val Val Glu Met Leu Thr Glu Lys Pro 550 555 560 565 CCT TGG GCA GAG TAT GAA GCT ATG GCT GCC ATT TTC AAG ATT GCC ACC 2142 Pro Trp Ala Glu Tyr Glu Ala Met Ala Ala He Phe Lys He Ala Thr 570 575 580 CAG CCT ACC AAT CCT CAG CTG CCC TCT CAC ATC TCA GAA CAC GGC AGG 2190 Gin Pro Thr Asn Pro Gin Leu Pro Ser His He Ser Glu His Gly Arg 585 590 595 GAC TTC CTG AGG CGC ATA TTT GTG GAA GCT CGT CAG AGA CCC TCA GCT 2238 Asp Phe Leu Arg Arg He Phe Val Glu Ala Arg Gin Arg Pro Ser Ala 600 605 610 GAG GAG CTG CTC ACA CAC CAC TTT GCA CAG CTA GTG TAC TGAGCTCTCA 2287 Glu Glu Leu Leu Thr His His Phe Ala Gin Leu Val Tyr 615 620 625 AGGCTATCAG GCTGCCAGCT GCCACCTGCT GAGCAGGCAA GGGGCTGCTG TCAGGCTCAG 2347 TGAAGTTGCT GCTTCTTCCA GGCAAGGCTA TGACCAGTGG AGCATCGGTC CAGCCATTGT 2407 TTGTCTGTGC CCCATCTGCC ACTGGGACTC AAAGCCAGGA TGGGATAGCT CTGGCATCAA 2467 GACTGGGAGC TCCAGCCTGT AAGACCCAAG AGCTTTAGCA CCTTAAGCTC AGTATGGCGG 2527 GAAGGGCTGG AAACAGTATG CAAGACTGCC ATGGGTCCTG CCTACCCTCA GATGTGTCCT 2587 AACACTGCAG ACAGCACTGA AGTCAAGAGG GACTGGGGCA CAGGAGGTCC TCAAGGGTAT 2647 GAATAGTGTT ACTTCATTCA GAGTGTTACT TTGTTTCTCT CCCAATGTTT GGAGACCACC 2707 AGCCTGTCTC TGGGCTGCAA GCCTGAGGTA AAGCCCAGCA TCCCCCAGCC AACAGAAGGT 2767 AGAGGTTTGG GCTACCCCAC TATAGCTTCC AGGTATTCGG TGTCAGTCCT GTCTTACCAA 2827 AGATGAATGA AGCAAATGTT ACACTGCCTT ATTCTGGGAA GGAGGAGCTA CTCGGATAAG 2887 CAGGGCCTGA GAGATGGAGC TGCCTCCAGA AACTGGGGAG ACCCAGTCTT GTCAATGCAA 2947 TTGTCTCTGT TTTACAAGTT GGAGTCACTC TTATGCTGTT CCCAGTTTTA AAACTGGAGA 3007 CTTTGCCCTC TGAGCTCTGG AGACCCATGT GGGCTTAGGC TTGGACTGGA TGGAAGAGCT 3067 GATGGCCTCT GCCCCTGGCC TG 3089 An MEKK protein of the present invention can also include an MEKK protein having at least a portion of the nucleic acid and/or amino acid sequence shown in Table 4 and represented by SEQ ID NO:7 and SEQ ID NO:8, respectively, and is referred to as MEKK 4. Table 4. AATTCGGCAC GAGAACCTAT CAGACATTGG CTGGCCAGTG TTTGAAATCC CCTCCCCTCG 60 GCCGTCCAAG GGCTACGAGC CAGAGGACGA GGTCGAGGAC ACGGAGGTTG AGCTGAGGGA 120 GCTGGAGAGC GGGACGGAGG AGAGTGACGA GGAGCCAACC CCCAGTCCGA GGGTGCCAGA 180 GCTCAGGCTG TCCACAGACA CCATCTTGGA CAGTCGCTCC CAGGGCTGCG TCTCCAGGAA 240 GCTGGAGAGG CTCGAGTCAG AGGAAGATTC CATAGGCTGG GGGACAGCGG ACTGTGGCCC 300 TGAAGCCAGC AGGCATTGTT TGACTTCTAT CTATAGACCA TTCGTGGACA AAGCACTGAA 360 GCAAATGGGG CTAAGAAAGT TAATTTTACG ACTTCATAAG CTTATGAATG GGTCCTTGCA 420 AAGAGCTCGT GTAGCTCTGG TGAAGGACGA CCGTCAGTGG AGTTCTCTGA CTTTCCAGGT 480 CCCATGTGGG GCTCGGATTA TGTGCAGTTG TCGGGAACAC CTCCTTCCTC AGAGCAGAAG 540 TGTAGCGCTG TGTCCTGGGA AGAACTGAGA GCCATGGACC TGCCTTCCTT TGAGCCCGCC 600 TTCCTGGTGC TCTGTCGGGT CCTGCTGAAC GTGATCCACG AGTGCCTGAA GCTGCGGCTG 660 GAACAGAGGC TGCCGGGGAG CCTTCCCTCT TGAGTATCAA ACAGCTAGTG CGAGAGTGTA 720 AAGAGGTCCT AAAGGGCGGG CTCCTG ATG AAG CAG TAT TAC CAG TTC ATG CTG 773 Met Lys Gin Tyr Tyr Gin Phe Met Leu 1 5 CAG GAG GTC CTG GGC GGA CTG GAG AAG ACC GAC TGC AAC ATG GAT GCC 821 Gin Glu Val Leu Gly Gly Leu Glu Lys Thr Asp Cys Asn Met Asp Ala 10 15 20 25 TTT GAG GAG GAC CTG CAG AAG ATG CTG ATG GTG TAT TTT GAT TAC ATG 869 Phe Glu Glu Asp Leu Gin Lys Met Leu Met Val Tyr Phe Asp Tyr Met 30 35 40 AGA AGC TGG ATC CAA ATG CTA CAG CAG TTA CCT CAG GCT TCC CAT AGC 917 Arg Ser Trp He Gin Met Leu Gin Gin Leu Pro Gin Ala Ser His Ser 45 50 55 TTA AAA AAC CTG CTA GAA GAG GAA TGG AAT TTC ACC AAA GAA ATA ACC 965 Leu Lys Asn Leu Leu Glu Glu Glu Trp Asn Phe Thr Lys Glu He Thr 60 65 70 CAT TAT ATC CGT GGC GGA GAA GCG CAG GCT GGA AAG CTT TTC TGT GAC 1013 His Tyr He Arg Gly Gly Glu Ala Gin Ala Gly Lys Leu Phe Cys Asp 75 80 85 ATC GCA GGG ATG CTG CTG AAA TCC ACA GGG AGC TTT CTG GAA TCC GGC 1061 He Ala Gly Met Leu Leu Lys Ser Thr Gly Ser Phe Leu Glu Ser Gly 90 95 100 105 CTG CAG GAG AGC TGT GCT GAG CTG TGG ACC AGN GCC GAC GAC AAC GGT 1109 Leu Gin Glu Ser Cys Ala Glu Leu Trp Thr Xaa Ala Asp Asp Asn Gly 110 115 120 GCT GCC GAC GAG CTA AGG AGA TCT GTC ATC GAG ATC AGC CGA GCA CTC 1157 Ala Ala Asp Glu Leu Arg Arg Ser Val He Glu He Ser Arg Ala Leu 125 130 135 AAG GAG CTC TTC CAC GAA GCC AGG GAA AGA GCC TCC AAG GCC CTG GGC 1205 Lys Glu Leu Phe His Glu Ala Arg Glu Arg Ala Ser Lys Ala Leu Gly 140 145 150 TTT GCT AAA ATG CTG AGG AAG GAC CTA GAA ATA GCA GCA GAG TTC GTG 1253 Phe Ala Lys Met Leu Arg Lys Asp Leu Glu He Ala Ala Glu Phe Val 155 160 165 CTA TCT GCA TCA GCC CGA GAG CTC CTG GAC GCT CTG AAA GCA AAG CAG 1301 Leu Ser Ala Ser Ala Arg Glu Leu Leu Asp Ala Leu Lys Ala Lys Gin 170 175 180 185 TAT GTT AAG GTA CAG ATT CCC GGG TTA GAG AAT TTG CAC GTG TTT GTC 1349 Tyr Val Lys Val Gin He Pro Gly Leu Glu Asn Leu His Val Phe Val 190 195 200 CCC GAC AGC CTC GCT GAG GAG AAG AAA ATT ATT TTG CAG CTA CTC AAT 1397 Pro Asp Ser Leu Ala Glu Glu Lys Lys He He Leu Gin Leu Leu Asn 205 210 215 GCT GCC ACA GGA AAG GAC TGC TCA AAG GAT CCA GAC GAC GTC TTC ATG 1445 Ala Ala Thr Gly Lys Asp Cys Ser Lys Asp Pro Asp Asp Val Phe Met 220 225 230 GAT GCC TTC CTG CTC CTG ACC AAG CAT GGG GAC CGA GCC CGT GAC TCA 1493 Asp Ala Phe Leu Leu Leu Thr Lys His Gly Asp Arg Ala Arg Asp Ser 235 240 245 GAA GAT GGC TGG GGC ACA TGG GAA GCT CGG GCT GTC AAA ATT GTG CCT 1541 Glu Asp Gly Trp Gly Thr Trp Glu Ala Arg Ala Val Lys He Val Pro 250 255 260 265 CAG GTG GAG ACT GTG GAC ACC CTG AGA AGC ATG CAG GTG GAC AAC CTT 1589 Gin Val Glu Thr Val Asp Thr Leu Arg Ser Met Gin Val Asp Asn Leu 270 275 280 CTG CTG GTT GTC ATG GAG TCT GCT CAC CTC GTA CTT CAG AGA AAA GCC 1637 Leu Leu Val Val Met Glu Ser Ala His Leu Val Leu Gin Arg Lys Ala 285 290 295 TTC CAG CAG TCC ATT GAG GGG CTG ATG ACT GTA CGC CAT GAG CAG ACA 1685 Phe Gin Gin Ser He Glu Gly Leu Met Thr Val Arg His Glu Gin Thr 300 305 310 TCT AGC CAG CCC ATC ATC GCC AAA GGT TTG CAG CAG CTC AAG AAC GAT 1733 Ser Ser Gin Pro He He Ala Lys Gly Leu Gin Gin Leu Lys Asn Asp 315 320 325 GCA CTT GAG CTA TGC AAC AGA ATC AGC GAT GCC ATC GAC CGT GTG GAC 1781 Ala Leu Glu Leu Cys Asn Arg He Ser Asp Ala He Asp Arg Val Asp 330 335 340 345 CAC ATG TTC ACC CTG GAG TTC GAT GCT GAG GTC GAG GAG TCT GAG TCG 1829 His Met Phe Thr Leu Glu Phe Asp Ala Glu Val Glu Glu Ser Glu Ser 350 355 360 GCC ACG CTG CAG CAG TAC TAC CGA GAA GCC ATG ATT CAG GGC TAC AAC 1877 Ala Thr Leu Gin Gin Tyr Tyr Arg Glu Ala Met He Gin Gly Tyr Asn 365 370 375 TTT GGG TTT GAG TAT CAT AAA GAA GTT GTT CGT TTG ATG TCT GGG GAA 1925 Phe Gly Phe Glu Tyr His Lys Glu Val Val Arg Leu Met Ser Gly Glu 380 385 390 TTC AGG CAG AAG ATA GGA GAC AAA TAT ATA ACG TTC GCC CAG AAG TGG 1973 Phe Arg Gin Lys He Gly Asp Lys Tyr He Thr Phe Ala Gin Lys Trp 395 400 405 ATG AAT TAC GTG CTG ACC AAA TGC GAG AGC GGC AGA GGC ACA AGA CCC 2021 Met Asn Tyr Val Leu Thr Lys Cys Glu Ser Gly Arg Gly Thr Arg Pro 410 415 420 425 AGA TGG GCC ACC CAA GGA TTT GAT TTC CTA CAA GCC ATT GAA CCT GCC 2069 Arg Trp Ala Thr Gin Gly Phe Asp Phe Leu Gin Ala He Glu Pro Ala 430 435 440 TTT ATT TCA GCT TTA CCA GAA GAT GAC TTC TTG AGT TTG CAA GCC CTG 2117 Phe He Ser Ala Leu Pro Glu Asp Asp Phe Leu Ser Leu Gin Ala Leu 445 450 455 ATG AAT GAG TGC ATC GGG CAC GTC ATA GGA AAG CCA CAC AGC CCT GTC 2165 Met Asn Glu Cys He Gly His Val He Gly Lys Pro His Ser Pro Val 460 465 470 ACA GCT ATC CAT CGG AAC AGC CCC CGC CCT GTG AAG GTG CCC CGA TGC 2213 Thr Ala He His Arg Asn Ser Pro Arg Pro Val Lys Val Pro Arg Cys 475 480 485 CAC AGT GAC CCT CCT AAC CCT CAC CTC ATC ATC CCG ACT CCA GAG GGA 2261 His Ser Asp Pro Pro Asn Pro His Leu He He Pro Thr Pro Glu Gly 490 495 500 505 TTC AGG GGT TCC AGT GTC CCT GAA AAC GAC CGC TTG GCC TCC ATA GCT 2309 Phe Arg Gly Ser Ser Val Pro Glu Asn Asp Arg Leu Ala Ser He Ala 510 515 520 GCA GAA CTG CAG TTC AGG TCT CTG AGT CGG CAC TCA AGC CCC ACG GAA 2357 Ala Glu Leu Gin Phe Arg Ser Leu Ser Arg His Ser Ser Pro Thr Glu 525 530 535 GAG CGA GAC GAG CCA GCG TAT CCT CGG AGT GAC TCA AGT GGA TCA ACT 2405 Glu Arg Asp Glu Pro Ala Tyr Pro Arg Ser Asp Ser Ser Gly Ser Thr 540 545 550 CGG AGA AGC TGG GAA CTT CGA ACA CTC ATC AGC CAG ACC AAA GAC TCG 2453 Arg Arg Ser Trp Glu Leu Arg Thr Leu He Ser Gin Thr Lys Asp Ser 555 560 565 GCC TCT AAG CAG GGG CCC ATA GAA GCT ATC CAG AAG TCA GTC CGA CTG 2501 Ala Ser Lys Gin Gly Pro He Glu Ala He Gin Lys Ser Val Arg Leu 570 575 580 585 TTT GAA GAG AGG AGG TAT CGA GAG ATG AGG AGA AAG AAT ATC ATC GGC 2549 Phe Glu Glu Arg Arg Tyr Arg Glu Met Arg Arg Lys Asn He He Gly 590 595 600 CAA GTG TGC GAT ACC CCT AAG TCC TAT GAT AAC GTC ATG CAT GTT GGA 2597 Gin Val Cys Asp Thr Pro Lys Ser Tyr Asp Asn Val Met His Val Gly 605 610 615 CTG AGG AAG GTG ACA TTT AAG TGG CAA AGA GGA AAC AAA ATT GGA GAA 2645 Leu Arg Lys Val Thr Phe Lys Trp Gin Arg Gly Asn Lys He Gly Glu 620 625 630 GGA CAG TAT GGA AAA GTA TAC ACC TGC ATC AGT GTT GAC ACA GGG GAG 2693 Gly Gin Tyr Gly Lys Val Tyr Thr Cys He Ser Val Asp Thr Gly Glu 635 640 645 CTG ATG GCC ATG AAG GAG ATT CGA TTT CAG CCT AAC GAC CAC AAG ACT 2741 Leu Met Ala Met Lys Glu He Arg Phe Gin Pro Asn Asp His Lys Thr 650 655 660 665 ATC AAG GAG ACT GCA GAC GAG TTG AAA ATA TTT GAA GGC ATC AAG CAC 2789 He Lys Glu Thr Ala Asp Glu Leu Lys He Phe Glu Gly He Lys His 670 675 680 CCC AAC CTG GTC CGG TAT TTT GGC GTG GAG CTT CAC AGG GAA GAG ATG 2837 Pro Asn Leu Val Arg Tyr Phe Gly Val Glu Leu His Arg Glu Glu Met 685 690 695 TAC ATC TTC ATG GAG TAC TGT GAT GAG GGT ACA CTA GAG GAG GTG TCA 2885 Tyr He Phe Met Glu Tyr Cys Asp Glu Gly Thr Leu Glu Glu Val Ser 700 705 710 CGA CTG GGC CTG CAG GAG CAC GTC ATC AGG TTA TAT ACC AAG CAG ATC 2933 Arg Leu Gly Leu Gin Glu His Val He Arg Leu Tyr Thr Lys Gin He 715 720 725 ACT GTC GCC ATC AAC GTC CTC CAT GAG CAC GGC ATC GTT CAC CGA GAC 2981 Thr Val Ala He Asn Val Leu His Glu His Gly He Val His Arg Asp 730 735 740 745 ATC AAA GGT GCC AAT ATC TTC CTT ACG TCA TCT GGA CTA ATC AAG CTG 3029 He Lys Gly Ala Asn He Phe Leu Thr Ser Ser Gly Leu He Lys Leu 750 755 760 GGA GAT TTT GGA TGC TCT GTA AAA CTT AAA AAC AAC GCC CAG ACC ATG 3077 Gly Asp Phe Gly Cys Ser Val Lys Leu Lys Asn Asn Ala Gin Thr Met 765 770 775 CCC GGA GAG GTG AAC AGC ACC CTA GGG ACA GCA GCT TAC ATG GCC CCT 3125 Pro Gly Glu Val Asn Ser Thr Leu Gly Thr Ala Ala Tyr Met Ala Pro 780 785 790 GAA GTT ATT ACC CGA GCC AAA GGA GAA GGC CAC GGA CGT GCG GCA GAT 3173 Glu Val He Thr Arg Ala Lys Gly Glu Gly His Gly Arg Ala Ala Asp 795 800 805 ATC TGG AGT CTG GGG TGC GTC GTC ATA GAG ATG GTG ACT GGC AAG CGG 3221 He Trp Ser Leu Gly Cys Val Val He Glu Met Val Thr Gly Lys Arg 810 815 820 825 CCT TGG CAT GAG TAT GAA CAC AAC TTT CAG ATT ATG TAC AAG GTG GGG 3269 Pro Trp His Glu Tyr Glu His Asn Phe Gin He Met Tyr Lys Val Gly 830 835 840 ATG GGA CAC AAG CCA CCA ATC CCG GAA AGG CTA AGC CCT GAA GGA AAG 3317 Met Gly His Lys Pro Pro He Pro Glu Arg Leu Ser Pro Glu Gly Lys 845 850 855 GCC TTT CTC TCG CAC TGC CTG GAA AGT GAC CCG AAG ATA CGG TGG ACA 3365 Ala Phe Leu Ser His Cys Leu Glu Ser Asp Pro Lys He Arg Trp Thr 860 865 870 GCC AGC CAG CTC CTC GAC CAC GCT TTT GTC AAG GTT TGC ACA GAT GAA 3413 Ala Ser Gin Leu Leu Asp His Ala Phe Val Lys Val Cys Thr Asp Glu 875 880 885 GAG T GAAGTGAACC AGTCCGTGGC CTAGTAGTGT GTGGACAGAA TCCCGTGATC 3467 Glu 890 ACTACTGTAT GTAATATTTA CATAAAGACT GCAGCGCAGG CGGCCTTCCT AACCTCCCAG 3527 GACTGAAGAC TACAGGGGTG ACAAGCCTCA CTTCTGCTGC TCCTGTCGCC TGCTGAGTGA 3587 CAGTGCTGAG GTTAAAGGAG CCGCACGTTA AGTGCCATTA CTACTGTACA CGGCCACCGC 3647 CTCTGTCCCC TCCGACCCTC TCGTGACTGA GAACCAACCG TGTCATCAGC ACAGTGTTTT 3707 TGAGCTCCTG GGGTTCAGAA GAACATGTAG TGTTCCCGGG TGTCCGGGAC GTTTATTTCA 3767 ACCTCCTGGT CGTTGGCTCT GACTGTGGAG CCTCCTTGTT CGAAAGCTGC AGGTTTGTTA 3827 TGCAAAGGCT CGTAAGTGAA GCTGAAGAAA AGGTTCTTTT TCAATAAATG GTTTATTTTA 3887 GGAAAGCGAA AAAAAAAAAA AAAAAA 3913 An MEKK protein of the present invention, referred to here as MEKK 5, includes an MEKK protein having at least a portion of the nucleic acid and/or amino acid sequence shown in Table 5 and represented by SEQ ID NO:9 and SEQ ID NO:10, respectively. Table 5. AAGAAGAAGG ACAGGGAGCA GAGGGGACAA GAAAACACGG CTGCTTTCTG GTTCAACCGA 60 TCGAACGAAC TGATCTGGTT AGAACTGCAG GCCTGGCACG CGGGCCGCAC CATCAATGAC 120 CAGGACCTCT TTCTCTACAC AGCCCGCCAG GCCATCCCAG ACATCATCAA TGAGATCCTC 180 ACCTTCAAAG TTAACTACGG GAGCATTGCC TTCTCCAGCA ATGGAGCCGG TTTCAACGGG 240 CCCTTGGTAG AAGGCCAGTG CAGAACCCCT CAGGAGACAA ACCGTGTGGG CTGCTCATCG 300 TACCACGAGC ACCTCCAGCG CCAGAGGGTC TCGTTTGAGC AGGTGAAGCG GATA ATG 357 Met 1 GAG CTG CTG GAG TAC ATG GAG GCA CTT TAC CCA TCC TTG CAG GCT CTG 405 Glu Leu Leu Glu Tyr Met Glu Ala Leu Tyr Pro Ser Leu Gin Ala Leu 5 10 15 CAG AAG GAC TAT GAA CGG TAC GCC GCC AAG GAC TTT GAG GAC AGA GTG 453 Gin Lys Asp Tyr Glu Arg Tyr Ala Ala Lys Asp Phe Glu Asp Arg Val 20 25 30 CAG GCG CTC TGC CTG TGG CTC AAC ATC ACG AAA GAT CTA AAT CAG AAG 501 Gin Ala Leu Cys Leu Trp Leu Asn He Thr Lys Asp Leu Asn Gin Lys 35 40 45 CTG CGG ATC ATG GGC ACC GTG CTG GGC ATC AAG TTC CTA TCA GAC ATT 549 Leu Arg He Met Gly Thr Val Leu Gly He Lys Phe Leu Ser Asp He 50 55 60 65 GGC TGG CCA GTG AAA GAA ATC CCC TCC CCT CGG CCG TCC AAG GGC TAC 597 Gly Trp Pro Val Lys Glu He Pro Ser Pro Arg Pro Ser Lys Gly Tyr 70 75 80 GAG CCA GAG GAC GAG GTC GAG GAC ACG GAG GTT GAG CTG AGG GAG CTG 645 Glu Pro Glu Asp Glu Val Glu Asp Thr Glu Val Glu Leu Arg Glu Leu 85 90 95 GAG AGC GGG ACG GAG GAG AGT GAC GAG GAG CCA ACC CCC AGT CCG AGG 693 Glu Ser Gly Thr Glu Glu Ser Asp Glu Glu Pro Thr Pro Ser Pro Arg 100 105 110 GTG CCA GAG CTC AGG CTG TCC ACA GAC ACC ATC TTG GAC AGT CGC TCC 741 Val Pro Glu Leu Arg Leu Ser Thr Asp Thr He Leu Asp Ser Arg Ser 115 120 125 CAG GGC TGC GTC TCC AGG AAG CTG GAG AGG CTC GAG TCA GAG GAA GAT 789 Gin Gly Cys Val Ser Arg Lys Leu Glu Arg Leu Glu Ser Glu Glu Asp 130 135 140 145 TCC ATA GGC TGG GGG ACA GCG GAC TGT GGC CCT GAA GCC AGC AGG CAT 837 Ser He Gly Trp Gly Thr Ala Asp Cys Gly Pro Glu Ala Ser Arg His 150 155 160 TGT TTG ACT TCT ATC TAT AGA CCA TTC GTG GAC AAA GCA CTG AAG CAA 885 Cys Leu Thr Ser He Tyr Arg Pro Phe Val Asp Lys Ala Leu Lys Gin 165 170 175 ATG GGG CTA AGA AAG TTA ATT TTA CGA CTT CAT AAG CTT ATG AAT GGG 933 Met Gly Leu Arg Lys Leu He Leu Arg Leu His Lys Leu Met Asn Gly 180 185 190 TCC TTG CAA AGA GCT CGT GTA GCT CTG GTG AAG GAC GAC CGT CCA GTG 981 Ser Leu Gin Arg Ala Arg Val Ala Leu Val Lys Asp Asp Arg Pro Val 195 200 205 GAG TTC TCT GAC TTT CCA GGT CCC ATG TGG GGC TCG GAT TAT GTG CAG 1029 Glu Phe Ser Asp Phe Pro Gly Pro Met Trp Gly Ser Asp Tyr Val Gin 210 215 220 225 TTG TCG GGA ACA CCT CCT TCC TCA GAG CAG AAG TGT AGC GCT GTG TCC 1077 Leu Ser Gly Thr Pro Pro Ser Ser Glu Gin Lys Cys Ser Ala Val Ser 230 235 240 TGG GAA GAA CTG AGA GCC ATG GAC CTG CCT TCC TTT GAG CCC GCC TTC 1125 Trp Glu Glu Leu Arg Ala Met Asp Leu Pro Ser Phe Glu Pro Ala Phe 245 250 255 CTG GTG CTC TGT CGG GTC CTG CTG AAC GTG ATC CAC GAG TGC CTG AAG 1173 Leu Val Leu Cys Arg Val Leu Leu Asn Val He His Glu Cys Leu Lys 260 265 270 CTG CGG CTG GAA CAG AGG CCT GCC GGG GAG CCT TCC CTC TTG AGT ATC 1221 Leu Arg Leu Glu Gin Arg Pro Ala Gly Glu Pro Ser Leu Leu Ser He 275 280 285 AAA CAG CTA GTG CGA GAG TGT AAA GAG GTC CTA AAG GGC GGG CTC CTG 1269 Lys Gin Leu Val Arg Glu Cys Lys Glu Val Leu Lys Gly Gly Leu Leu 290 295 300 305 ATG AAG CAG TAT TAC CAG TTC ATG CTG CAG GAG GTC CTG GGC GGA CTG 1317 Met Lys Gin Tyr Tyr Gin Phe Met Leu Gin Glu Val Leu Gly Gly Leu 310 315 320 GAG AAG ACC GAC TGC AAC ATG GAT GCC TTT GAG GAG GAC CTG CAG AAG 1365 Glu Lys Thr Asp Cys Asn Met Asp Ala Phe Glu Glu Asp Leu Gin Lys 325 330 335 ATG CTG ATG GTG TAT TTT GAT TAC ATG AGA AGC TGG ATC CAA ATG CTA 1413 Met Leu Met Val Tyr Phe Asp Tyr Met Arg Ser Trp He Gin Met Leu 340 345 350 CAG CAG TTA CCT CAG GCT TCC CAT AGC TTA AAA AAC CTG CTA GAA GAG 1461 Gin Gin Leu Pro Gin Ala Ser His Ser Leu Lys Asn Leu Leu Glu Glu 355 360 365 GAA TGG AAT TTC ACC AAA GAA ATA ACC CAT TAT ATC CGT GGC GGA GAA 1509 Glu Trp Asn Phe Thr Lys Glu He Thr His Tyr He Arg Gly Gly Glu 370 375 380 385 GCG CAG GCT GGA AAG CTT TTC TGT GAC ATC GCA GGG ATG CTG CTG AAA 1557 Ala Gin Ala Gly Lys Leu Phe Cys Asp He Ala Gly Met Leu Leu Lys 390 395 400 TCC ACA GGG AGC TTT CTG GAA TCC GGC CTG CAG GAG AGC TGT GCT GAG 1605 Ser Thr Gly Ser Phe Leu Glu Ser Gly Leu Gin Glu Ser Cys Ala Glu 405 410 415 CTG TGG ACC AGC GCC GAC GAC AAC GGT GCT GCC GAC GAG CTA AGG AGA 1653 Leu Trp Thr Ser Ala Asp Asp Asn Gly Ala Ala Asp Glu Leu Arg Arg 420 425 430 TCT GTC ATC GAG ATC AGC CGA GCA CTC AAG GAG CTC TTC CAC GAA GCC 1701 Ser Val He Glu He Ser Arg Ala Leu Lys Glu Leu Phe His Glu Ala 435 440 445 AGG GAA AGA GCC TCC AAG GCC CTG GGC TTT GCT AAA ATG CTG AGG AAG 1749 Arg Glu Arg Ala Ser Lys Ala Leu Gly Phe Ala Lys Met Leu Arg Lys 450 455 460 465 GAC CTA GAA ATA GCA GCA GAG TTC GTG CTA 1797 Asp Leu Glu He Ala Ala Glu Phe Val Leu 470 475 CTC CTG GAC GCT CTG AAA GCA AAG CAG TAT 1845 Leu Leu Asp Ala Leu Lys Ala Lys Gin Tyr 485 490 GGG TTA GAG AAT TTG CAC GTG TTT GTC CCC 1893 Gly Leu Glu Asn Leu His Val Phe Val Pro 500 505 AAG AAA ATT ATT TTG CAG CTA CTC AAT GCT 1941 Lys Lys He He Leu Gin Leu Leu Asn Ala 515 520 TCA AAG GAT CCA GAC GAC GTC TTC ATG GAT 1989 Ser Lys Asp Pro Asp Asp Val Phe Met Asp 530 535 AAG CAT GGG GAC CGA GCC CGT GAC TCA GAA 2037 Lys His Gly Asp Arg Ala Arg Asp Ser Glu 550 555 GAA GCT CGG GCT GTC AAA ATT GTG CCT CAG 2085 Glu Ala Arg Ala Val Lys He Val Pro Gin 565 570 CTG AGA AGC ATG CAG GTG GAC AAC CTT CTG 2133 Leu Arg Ser Met Gin Val Asp Asn Leu Leu 580 585 GCT CAC CTC GTA CTT CAG AGA AAA GCC TTC 2181 Ala His Leu Val Leu Gin Arg Lys Ala Phe 595 600 CTG ATG ACT GTA CGC CAT GAG CAG ACA TCT 2229 Leu Met Thr Val Arg His Glu Gin Thr Ser 610 615 AAA GGT TTG CAG CAG CTC AAG AAC GAT GCA 2277 Lys Gly Leu Gin Gin Leu Lys Asn Asp Ala 630 635 ATC AGC GAT GCC ATC GAC CGT GTG GAC CAC 2325 He Ser Asp Ala He Asp Arg Val Asp His 645 650 GAT GCT GAG GTC GAG GAG TCT GAG TCG GCC 2373 Asp Ala Glu Val Glu Glu Ser Glu Ser Ala 660 665 CGA GAA GCC ATG ATT CAG GGC TAC AAC TTT 2421 Arg Glu Ala Met He Gin Gly Tyr Asn Phe 675 680 GAA GTT GTT CGT TTG ATG TCT GGG GAA TTC 2469 Glu Val Val Arg Leu Met Ser Gly Glu Phe 690 695 AAA TAT ATA AGC TTC GCC CAG AAG TGG ATG 2517 Lys Tyr He Ser Phe Ala Gin Lys Trp Met 710 715 TGC GAG AGC GGC AGA GGC ACA AGA CCC AGA 2565 Cys Glu Ser Gly Arg Gly Thr Arg Pro Arg 725 730 GAT TTC CTA CAA GCC ATT GAA CCT GCC TTT 2613 Asp Phe Leu Gin Ala He Glu Pro Ala Phe 740 745 GAT GAC TTC TTG AGT TTG CAA GCC CTG ATG AAT GAG TGC ATC GGG CAC 2661 Asp Asp Phe Leu Ser Leu Gin Ala Leu Met Asn Glu Cys He Gly His 755 760 765 GTC ATA GGA AAG CCA CAC AGC CCT GTC ACA GCT ATC CAT CGG AAC AGC 2709 Val He Gly Lys Pro His Ser Pro Val Thr Ala He His Arg Asn Ser 770 775 780 785 CCC CGC CCT GTG AAG GTG CCC CGA TGC CAC AGT GAC CCT CCT AAC CCT 2757 Pro Arg Pro Val Lys Val Pro Arg Cys His Ser Asp Pro Pro Asn Pro 790 795 800 CAC CTC ATC ATC CCG ACT CCA GAG GGA TTC AGC ACC CGG AGC GTG CCT 2805 His Leu He He Pro Thr Pro Glu Gly Phe Ser Thr Arg Ser Val Pro 805 810 815 2853 2901 2949 TCC AGT GTC CCT GAA AAC GAC CGC TTG GCC TCC ATA GCT GCA GAA CTG 2997 Ser Ser Val Pro Glu Asn Asp Arg Leu Ala Ser He Ala Ala Glu Leu 870 875 880 CAG TTC AGG TCT CTG AGT CGG CAC TCA AGC CCC ACG GAA GAG CGA GAC 3045 Gin Phe Arg Ser Leu Ser Arg His Ser Ser Pro Thr Glu Glu Arg Asp 885 890 895 GAG CCA GCG TAT CCT CGG AGT GAC TCA AGT GGA TCA ACT CGG AGA AGC 3093 Glu Pro Ala Tyr Pro Arg Ser Asp Ser Ser Gly Ser Thr Arg Arg Ser 900 905 910 TGG GAA CTT CGA ACA CTC ATC AGC CAG ACC AAA GAC TCG GCC TCT AAG 3141 Trp Glu Leu Arg Thr Leu He Ser Gin Thr Lys Asp Ser Ala Ser Lys 915 920 925 CAG GGG CCC ATA GAA GCT ATC CAG AAG TCA GTC CGA CTG TTT GAA GAG 3189 Gin Gly Pro He Glu Ala He Gin Lys Ser Val Arg Leu Phe Glu Glu 930 935 940 945 AGG AGG TAT CGA GAG ATG AGG AGA AAG AAT ATC ATC GGC CAA GTG TGC 3237 Arg Arg Tyr Arg Glu Met Arg Arg Lys Asn He He Gly Gin Val Cys 950 955 960 GAT ACC CCT AAG TCC TAT GAT AAC GTC ATG CAT GTT GGA CTG AGG AAG 3285 Asp Thr Pro Lys Ser Tyr Asp Asn Val Met His Val Gly Leu Arg Lys 965 970 975 GTG ACA TTT AAG TGG CAA AGA GGA AAC AAA ATT GGA GAA GGA CAG TAT 3333 Val Thr Phe Lys Trp Gin Arg Gly Asn Lys He Gly Glu Gly Gin Tyr 980 985 990 GGA AAA GTA TAC ACC TGC ATC AGT GTT GAC ACA GGG GAG CTG ATG GCC 3381 Gly Lys Val Tyr Thr Cys He Ser Val Asp Thr Gly Glu Leu Met Ala 995 1000 1005 ATG AAG GAG ATT CGA TTT CAG CCT AAC GAC CAC AAG ACT ATC AAG GAG 3429 Met Lys Glu He Arg Phe Gin Pro Asn Asp His Lys Thr He Lys Glu 1010 1015 1020 1025 ACT GCA GAC GAG TTG AAA ATA TTT GAA GGC ATC AAG CAC CCC AAC CTG 3477 Thr Ala Asp Glu Leu Lys He Phe Glu Gly He Lys His Pro Asn Leu 1030 1035 1040 GTC CGG TAT TTT GGC GTG GAG CTT CAC AGG GAA GAG ATG TAC ATC TTC 3525 Val Arg Tyr Phe Gly Val Glu Leu His Arg Glu Glu Met Tyr He Phe 1045 1050 1055 ATG GAG TAC TGT GAT GAG GGT ACA CTA GAG GAG GTG TCA CGA CTG GGC 3573 Met Glu Tyr Cys Asp Glu Gly Thr Leu Glu Glu Val Ser Arg Leu Gly 1060 1065 1070 CTG CAG GAG CAC GTC ATC AGG TTA TAT ACC AAG CAG ATC ACT GTC GCC 3621 Leu Gin Glu His Val He Arg Leu Tyr Thr Lys Gin He Thr Val Ala 1075 1080 1085 ATC AAC GTC CTC CAT GAG CAC GGC ATC GTT CAC CGA GAC ATC AAA GGT 3669 He Asn Val Leu His Glu His Gly He Val His Arg Asp He Lys Gly 1090 1095 1100 1105 GCC AAT ATC TTC CTT ACG TCA TCT GGA CTA ATC AAG CTG GGA GAT TTT 3717 Ala Asn He Phe Leu Thr Ser Ser Gly Leu He Lys Leu Gly Asp Phe 1110 1115 1120 GGA TGC TCT GTA AAA CTT AAA AAC AAC GCC CAG ACC ATG CCC GGA GAG 3765 Gly Cys Ser Val Lys Leu Lys Asn Asn Ala Gin Thr Met Pro Gly Glu 1125 1130 1135 GTG AAC AGC ACC CTA GGG ACA GCA GCT TAC ATG GCC CCT GAA GTT ATT 3813 Val Asn Ser Thr Leu Gly Thr Ala Ala Tyr Met Ala Pro Glu Val He 1140 1145 1150 ACC CGA GCC AAA GGA GAA GGC CAC GGA CGT GCG GCA GAT ATC TGG AGT 3861 Thr Arg Ala Lys Gly Glu Gly His Gly Arg Ala Ala Asp He Trp Ser 1155 1160 1165 CTG GGG TGC GTC GTC ATA GAG ATG GTG ACT GGC AAG CGG CCT TGG CAT 3909 Leu Gly Cys Val Val He Glu Met Val Thr Gly Lys Arg Pro Trp His 1170 1175 1180 1185 GAG TAT GAA CAC AAC TTT CAG ATT ATG TAC AAG GTG GGG ATG GGA CAC 3957 Glu Tyr Glu His Asn Phe Gin He Met Tyr Lys Val Gly Met Gly His 1190 1195 1200 AAG CCA CCA ATC CCG GAA AGG CTA AGC CCT GAA GGA AAG GCC TTT CTC 4005 Lys Pro Pro He Pro Glu Arg Leu Ser Pro Glu Gly Lys Ala Phe Leu 1205 1210 1215 TCG CAC TGC CTG GAA AGT GAC CCG AAG ATA CGG TGG ACA GCC AGC CAG 4053 Ser His Cys Leu Glu Ser Asp Pro Lys He Arg Trp Thr Ala Ser Gin 1220 1225 1230 CTC CTC GAC CAC GCT TTT GTC AAG GTT TGC ACA GAT GAA GAG 4095 Leu Leu Asp His Ala Phe Val Lys Val Cys Thr Asp Glu Glu 1235 1240 1245 TGAAGTGAAC CAGTCCGTGG CCTAGTAGTG TGTGGACAGA ATCCCGTGAT CACTACTGTA 4155 TGTAATATTT ACATAAAGAC TGCAGCGCAG GCGGCCTTCC TAACCTCCCA GGACTGAAGA 4215 CTACAGGGGT GACAAGCCTC ACTTCTGCTG CTCCTGTCGC CTGCTGAGTG ACAGTGCTGA 4275 GGTTAAAGGA GCCGCACGTT AAGTGCCATT ACTACTGTAC ACGGCCACCG CCTCTGTCCC 4335 CTCCGACCCT CTCGTGACTG AGAACCAACC GTGTCATCAG CACAGTGTTT TTGAGCTCCT 4395 GGGGTTCAGA AGAACATGTA GTGTTCCCGG GTGTCCGGGA CGTTTATTTC AACCTCCTGG 4455 TCGTTGGCTC TGACTGTGGA GCCTCCTTGT TCGAAAGCTG CAGGTTTGTT ATGCAAAGGC 4515 TCGTAAGTGA AGCTGAAGAA AAGGTTCTTT TTCAATAAAT GGTTTATTTT AGGAAAGCGA 4575 AAAAAAAAAA AAAAAAA 4592 MEKK 5 represents a splice variant of MEKK 4. The splice insert is shown by the underlined portion of the sequence shown in Table 5. The amino acid sequences for MEKK 2 and MEKK 3 compared with the amino acid sequence of MEKK 1 are shown in Table 6. Table 6. IWTAVPAVFSi VTllLI_AS(STHπRM_UWUIAIAD__VEIAEVI0L-n^DTVDα«_OSL MEKK 1 mDOOALNSINQDI 2 MDEQEALDSIMKDLVALOKS RTRL- 3 AVAPTSCI_ENSSLEHTVH ECTGKGLSATRLSASSEDISD UWWSW3_IJ>SSTTTEQP__P 1 ΛVLHI I>V-_QHYLYI_l-P_-KQNLHH_-I Nm^ 2 S--GY_rm_Niα)TGHPHRg-_OVRII(FEHNGERRI-IAFSt_PVRY__DVEHi VTTVFG__IPI-D 3 AWTKGWHSOCLHSS-PLSHAQ_J)FPAPSAPtSSAPSVPOISI_ΗRPtW_Tn>CKIPSASP 1 AFG Q SWLHYTNNELVIPLTTQDDLDKAVELLDRSIHNKSL-KILLWIIGST M-TNLEP 2 LHYMHHELSILLI0«_OD__DKAIDILDR-KSMKSLRILLLS__0RHHTSSSPHSGV__R(_VRI 3 QTQRKFSLQFQRMCSEHRDSOQLSPVFTQS-RPPPSSN I HRPKPSRPVPGSTSKLGDATK 1 SPSPEDLNNTPLGAERiα RLSVV__PPt.R--DRSS£PPGYIPDILH Q IARNGSFTSINSEG 2 KPSQSAGDINTIY Q APEPRSRHLSVSS Q NPGRSSPPPGYVPERQQHIARQGSYTSINSEG 3 SSMTLDLGSASRCDDSFGGGGNSGNAVIPSDETVFTPVEDKCRLDVNTELNSSIEDLLEA 1 EFIPESMO Q -MLDPLSLSSPENSGSGSCPSLDSPLDGESYPKSRMPRAQSYPDNHQEFTD 2 EF I PETSE Q CHLDPLSSAENSLSGSC Q SLDRSADSPSFRKSQMSRARSFPDNR- --ECSD 3 SMPSSDTTVTFKSEVAVLSPEKAENDDTYKDDVNHNQKCKEKMEAEEEEALAIAMAMSAS 1 YDNPI FEKFGKGGTYPRRYHVSYHHQEYNDGRKTFPRARRTQGTSFRSPVSFSPTDHSLS 2 K RETQLYDKGVKGGTYPRRYHVSVHHKDYNDGRRTFPR I RRHQGNLFTLVPSSRSL 3 Q DALPIVPQLQVENGEDI I I IQQDTPETLPGHTKAKQPYREDABILKGOQIGLGAFSSCY 1 TSSGSSVFTPE YDDSR I RRRGSD I DNPTLTVTD I SPPSRSPRAPTHURLO LLGOGAFGI- 2 STNGENHGVAVQYLDPRGRLRSADSE-.ALTVQERWVPTKSPSAPmWRR03.LGQ-_AF.-R 3 _AQDVGTGT--HA\n QVTYVRHTSSE--EEVVEALREEIRIWGHLMHPI.IIRMLGATCEI SW 1 VYLCYDVDTGRELAVKQVQFMPESPETSKEVIIALECEIQLLPILLHERIVQYYGCLRDPQ 2 VYLCYDVDTGRELASKQVQFDPDSPETSKEVSALECEIQLLKMLOHERIVQYYGCLRORA 3 YMLFIEmAGGSVAHLLSKYGAFgSWIHYTEQLLRGLSYLHEM— Q-I IHRDVKGΛHL 1 EKTLSIFMELSPGGSIICDQLI AYGALTENVTRKYTRQILEGVHYLHSW.IVHRDII --AMI 2 EKILTIFHEYMP_a_SVI-DQL--AYGALTESVTRI YTRQILEGMSYLHSWHIVHRDlK--A>II 3 LIDSTGQ-RLRIADFGAAARLASIC-GTGAGEFQGQLLGTIAFMAPEVLRGQQYGRSCDVU 1 LR0STGMIKLGDFGASI-RLQT1CLSGTGHKSVTG-PY UHSPEVISGEGYGRKADIU 2 LRDSAGMVKLGDFGASI-RLQT1CMSGTGIRSVTGTPY UHSPEVISGEGYGRKADVU 3 SVGCAI IEMACAKPPUHAEKHSHHLALI FICIASATTAPSIPSHLSPGLRDVAVRCLELQP 1 SVACTWt-MLTEI-PPU-AEFI-A-MAA- 1 FKIATQPTMPKLPPHVSDYTRDFLKRI FVEAK 2 SLGCrrVVEMLTEI PPU-AEYa-MAA-IFKIATQPTHPQLPSHISEHGRDFLRRIFVEAR 3 QDRPPSRE-LLKHPVFRTTU 1 L-RP-SAEELLRHMFVHYH Q-RP-SAEELLTHHFAQLVY Bold Amino Terminus- Reςpulatory Domain Underline sequence- Rerjulatory hinσe Sequence Bold Italics- Catalytic Domain Table 7 shows the amino acid sequence of the kinase domain of MEKK 4 compared with the kinase domains of MEKK 1, MEKK 2 and MEKK 3. Table 7 . ..IRFQPNDHKTIKETADEELI.IFEGIKHPNLVRYFGV_.ELHREEM.YI MEKK4 TYVRNTSSEQEEWEALREEIRMHGHLNHPNIIRMLGATCEKSNYNLFIE MEKK1 QVQFNPESPETSKEVNALECEIQLLKNLLHERIVQYYGCLRDPQEKTLSI MEKK2 QVQFDPDSPETSKEVSALECEIQLLKNLQHERIVQYYGCLRDRAEKILTI MEKK3 IFMEYCDEGTLEEVSRLGLQEHV.I.RLYTKQITVAINVLHEHGNV HEKK4 .UMAGGSVAHLLSKYGAFKESW.IN..YTEQLLRGLSYLHENQII MEKK1 .FMELSPGGSIKDQLKAYGALTENVTRKYTRQILEGVHYLHSNMIV MEKK2 .FMEYMPGGSVKDQLKAYGALTESVTRKYTRQILEGMSYLHSNMIV MEKK3 The foregoing SEQ ID NO's represent sequences deduced according to methods disclosed in the Examples. It should be noted that since nucleic acid and amino acid sequencing technology is not entirely error-free, the foregoing SEQ ID NO's, at best, represent apparent nucleic acid and amino acid sequences of MEKK proteins of the present invention. According to the present invention, an MEKK protein of the present invention can include MEKK proteins that have undergone post-translational modification. Such modification can include, for example, glycosylation (e.g., including addition of N-linked and/or O-linked oligosaccharides) or post-translational conformational changes or post-translational deletions. Another embodiment of the present invention is an isolated nucleic acid molecule capable of hybridizing, under stringent conditions, with an MEKK protein gene encoding an MEKK protein of the present invention. In accordance with the present invention, an isolated nucleic acid molecule is a nucleic acid molecule that has been removed from its natural milieu (i.e., that has been subject to human manipulation) . As such, "isolated" does not reflect the extent to which the nucleic acid molecule has been purified. An isolated nucleic acid molecule can include DNA, RNA, or derivatives of either DNA or RNA. An isolated nucleic acid molecule of the present invention can be obtained from its natural source either as an entire (i.e., complete) gene or a portion thereof capable of forming a stable hybrid with that gene. As used herein, the phrase "at least a portion of" an entity refers to an amount of the entity that is at least sufficient to have the functional aspects of that entity. For example, at least a portion of a nucleic acid sequence, as used herein, is an amount of a nucleic acid sequence capable of forming a stable hybrid with a particular desired gene (e.g., MEKK genes) under stringent hybridization conditions. An isolated nucleic acid molecule of the present invention can also be produced using recombinant DNA technology (e.g., polymerase chain reaction (PCR) amplification, cloning) or chemical synthesis. Isolated MEKK protein nucleic acid molecules include natural nucleic acid molecules and homologues thereof, including, but not limited to, natural allelic variants and modified nucleic acid molecules in which nucleotides have been inserted, deleted, substituted, and/or inverted in such a manner that such modifications do not substantially interfere with the nucleic acid molecule's ability to encode an MEKK protein of the present invention or to form stable hybrids under stringent conditions with natural nucleic acid molecule isolates of MEKK. Preferred modifications to an MEKK protein nucleic acid molecule of the present invention include truncating a full-length MEKK protein nucleic acid molecule by, for example: deleting at least a portion of an MEKK protein nucleic acid molecule encoding a regulatory domain (examples illustrated in Table 6) to produce a constitutively active MEKK protein; deleting at least a portion of an MEKK protein nucleic acid molecule encoding a catalytic domain (examples illustrated in Table 6) to produce an inactive MEKK protein; and modifying the MEKK protein to achieve desired inactivation and/or stimulation of the protein, for example, substituting a codon encoding a lysine residue in the catalytic domain (i.e., phosphotransferase domain) with a methionine residue to inactivate the catalytic domain. A preferred truncated MEKK nucleic acid molecule encodes a form of an MEKK protein containing a catalytic domain but that lacks a regulatory domain. Preferred catalytic domain truncated MEKK nucleic acid molecules encode residues from about 352 to about 672 of MEKK 1, from about 352 to about 619 of MEKK 2, from about 358 to about 626 of MEKK 3, from about 811 to about 1195 of MEKK 4 or from about 863 to about 1247 of MEKK 5. Another preferred truncated MEKK nucleic acid molecule encodes a form of an MEKK protein comprising an NH 2 -terminal regulatory domain a catalytic domain but lacking a catalytic domain. Preferred regulatory domain truncated MEKK nucleic acid molecules encode residues from about 1 to about 369 for MEKK 1, from about 1 to about 335 for MEKK 2, from about 1 to about 360 for MEKK 3, from about 1 to about 825 for MEKK 4 and from about 1 to about 875 for MEKK 5, thereby removing the regulatory domain to form the truncated MEKK molecule. An isolated nucleic acid molecule of the present invention can include a nucleic acid sequence that encodes at least one MEKK protein of the present invention, examples of such proteins being disclosed herein. Although the phrase "nucleic acid molecule" primarily refers to the physical nucleic acid molecule and the phrase "nucleic acid sequence" primarily refers to the sequence of nucleotides that comprise the nucleic acid molecule, the two phrases can be used interchangeably. As heretofore disclosed, MEKK proteins of the present invention include, but are not limited to, proteins having full-length MEKK protein coding regions, portions thereof, and other MEKK protein homologues. As used herein, an MEKK protein gene includes all nucleic acid sequences related to a natural MEKK protein gene such as regulatory regions that control production of an MEKK protein encoded by that gene (including, but not limited to, transcription, translation or post-translation control regions) as well as the coding region itself. A nucleic acid molecule of the present invention can be an isolated natural MEKK protein nucleic acid molecule or a homologue thereof. A nucleic acid molecule of the present invention can include one or more regulatory regions, full- length or partial coding regions, or combinations thereof. The minimal size of an MEKK protein nucleic acid molecule of the present invention is the minimal size capable of forming a stable hybrid under stringent hybridization conditions with a corresponding natural gene. An MEKK protein nucleic acid molecule homologue can be produced using a number of methods known to those skilled in the art (see, e.g., Sambrook et al., ibid. ) . For example, nucleic acid molecules can be modified using a variety of techniques including, but not limited to, classic mutagenesis techniques and recombinant DNA techniques, such as site-directed mutagenesis, chemical treatment of a nucleic acid molecule to induce mutations, restriction enzyme cleavage of a nucleic acid fragment, ligation of nucleic acid fragments, polymerase chain reaction (PCR) amplification and/or mutagenesis of selected regions of a nucleic acid sequence, synthesis of oligonucleotide mixtures and ligation of mixture groups to "build" a mixture of nucleic acid molecules and combinations thereof. Nucleic acid molecule homologues can be selected from a mixture of modified nucleic acids by screening for the function of the protein encoded by the nucleic acid (e.g., the ability of a homologue to phosphorylate MEK protein or JEK protein) and/or by hybridization with isolated MEKK protein nucleic acids under stringent conditions. One embodiment of the present invention is an MEKK protein nucleic acid molecule capable of encoding at least a portion of an MEKK protein, or a homologue thereof, as described herein. A preferred nucleic acid molecule of the present invention includes, but is not limited to, a nucleic acid molecule that encodes a protein having at least a portion of an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10, or homologues thereof. A preferred nucleic acid molecule of the present invention is capable of hybridizing under stringent conditions to a nucleic acid that encodes at least a portion of an MEKK protein, or a homologue thereof. Also preferred is an MEKK protein nucleic acid molecule that includes a nucleic acid sequence having at least about 50%, preferably at least about 75%, and more preferably at least about 85% homology with the corresponding region(s) of the nucleic acid sequence encoding the catalytic domain of an MEKK protein, or a homologue thereof. Also preferred is an MEKK protein nucleic acid molecule that includes a nucleic acid sequence having at least about 20%, preferably at least about 30%, and more preferably at least about 40% homology with the corresponding region(s) of the nucleic acid sequence encoding the NH 2 -terminal regulatory domain of an MEKK protein, or a homologue thereof. A particularly preferred nucleic acid sequence is a nucleic acid sequence having at least about 50%, preferably at least about 75%, and more preferably at least about 85% homology with a nucleic acid sequence encoding the catalytic domain of an amino acid sequence represented by SEQ ID NO:2, SEQ ID N0:4, SEQ ID N0:6, SEQ ID N0:8 and SEQ ID NO:10. Another particularly preferred nucleic acid sequence is a nucleic acid sequence having at least about 20%, preferably at least about 30%, and more preferably at least about 40% homology with a nucleic acid sequence encoding the NH 2 - terminal regulatory domain of an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10. Such nucleic acid molecules can be a full-length gene and/or a nucleic acid molecule encoding a full-length protein, a hybrid protein, a fusion protein, a multivalent protein or a truncation fragment. More preferred nucleic acid molecules of the present invention comprise isolated nucleic acid molecules having a nucleic acid sequence as represented by SEQ ID N0:1, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 or SEQ ID NO:9. Knowing a nucleic acid molecule of an MEKK protein of the present invention allows one skilled in the art to make copies of that nucleic acid molecule as well as to obtain additional portions of MEKK protein-encoding genes (e.g., nucleic acid molecules that include the translation start site and/or transcription and/or translation control regions) , and/or MEKK protein nucleic acid molecule homologues. Knowing a portion of an amino acid sequence of an MEKK protein of the present invention allows one skilled in the art to clone nucleic acid sequences encoding such an MEKK protein. The present invention also includes nucleic acid molecules that are oligonucleotides capable of hybridizing, under stringent conditions, with complementary regions of other, preferably longer, nucleic acid molecules of the present invention that encode at least a portion of an MEKK protein, or a homologue thereof. A preferred oligonucleotide is capable of hybridizing, under stringent conditions, with a nucleic acid molecule that is capable of encoding at least a portion of an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10, or homologues thereof. A more preferred oligonucleotide is capable of hybridizing to a nucleic acid molecule having a nucleic acid sequence as represented by SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and SEQ ID NO:9, or complements thereof. Oligonucleotides of the present invention can be RNA, DNA, or derivatives of either. The minimal size of such oligonucleotides is the size required to form a stable hybrid between a given oligonucleotide and the complementary sequence on another nucleic acid molecule of the present invention. Minimal size characteristics are disclosed herein. The size of the oligonucleotide must also be sufficient for the use of the oligonucleotide in accordance with the present invention. Oligonucleotides of the present invention can be used in a variety of applications including, but not limited to, as probes to identify additional nucleic acid molecules, as primers to amplify or extend nucleic acid molecules or in therapeutic applications to inhibit, for example, expression of MEKK proteins by cells. Such therapeutic applications include the use of such oligonucleotides in, for example, antisense-, triplex formation-, ribozyme- and/or RNA drug- based technologies. The present invention, therefore, includes use of such oligonucleotides and methods to interfere with the production of MEKK proteins. In one embodiment, an isolated MEKK protein of the present invention is produced by culturing a cell capable of expressing the protein under conditions effective to produce the protein, and recovering the protein. A preferred cell to culture is a recombinant cell that is capable of expressing the MEKK protein, the recombinant cell being produced by transforming a host cell with one or more nucleic acid molecules of the present invention. Transformation of a nucleic acid molecule into a cell can be accomplished by any method by which a nucleic acid molecule can be inserted into the cell. Transformation techniques include, but are not limited to, transfection, electroporation, microinjection, lipofection, adsorption, and protoplast fusion. A recombinant cell may remain unicellular or may grow into a tissue, organ or a multicellular organism. Transformed nucleic acid molecules of the present invention can remain extrachromosomal or can integrate into one or more sites within a chromosome of the transformed (i.e., recombinant) cell in such a manner that their ability to be expressed is retained. The present invention also includes a recombinant vector which includes at least one MEKK protein nucleic acid molecule of the present invention inserted into any vector capable of delivering the nucleic acid molecule into a host cell. Such a vector contains heterologous nucleic acid sequences, for example nucleic acid sequences that are not naturally found adjacent to MEKK protein nucleic acid molecules of the present invention. The vector can be either RNA or DNA, and either prokaryotic or eukaryotic, and is typically a virus or a plasmid. Recombinant vectors can be used in the cloning, sequencing, and/or otherwise manipulating of MEKK protein nucleic acid molecules of the present invention. One type of recombinant vector, herein referred to as a recombinant molecule and described in more detail below, can be used in the expression of nucleic acid molecules of the present invention. Preferred recombinant vectors are capable of replicating in the transformed cell. Preferred nucleic acid molecules to insert into a recombinant vector includes a nucleic acid molecule that encodes at least a portion of an MEKK protein, or a homologue thereof. A more preferred nucleic acid molecule to insert into a recombinant vector includes a nucleic acid molecule encoding at least a portion of an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and/or SEQ ID NO:10, or homologues thereof. An even more preferred nucleic acid molecule to insert into a recombinant vector includes a nucleic acid molecule represented by SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and/or SEQ ID NO:9, or complements thereof. Suitable host cells for transforming a cell can include any cell capable of producing MEKK proteins of the present invention after being transformed with at least one nucleic acid molecule of the present invention. Host cells can be either untransformed cells or cells that are already transformed with at least one nucleic acid molecule. Suitable host cells of the present invention can include bacterial, fungal (including yeast) , insect, animal and plant cells. Preferred host cells include bacterial, yeast, insect and mammalian cells, with mammalian cells being particularly preferred. A recombinant cell is preferably produced by transforming a host cell with one or more recombinant molecules, each comprising one or more nucleic acid molecules of the present invention operatively linked to an expression vector containing one or more transcription control sequences. The phrase operatively linked refers to insertion of a nucleic acid molecule into an expression vector in a manner such that the molecule is able to be expressed when transformed into a host cell. As used herein, an expression vector is a DNA or RNA vector that is capable of transforming a host cell and of effecting expression of a specified nucleic acid molecule. Preferably, the expression vector is also capable of replicating within the host cell. Expression vectors can be either prokaryotic or eukaryotic, and are typically viruses or plasmids. Expression vectors of the present invention include any vectors that function (i.e., direct gene expression) in recombinant cells of the present invention, including in bacterial, fungal, insect, animal, and/or plant cells. As such, nucleic acid molecules of the present invention can be operatively linked to expression vectors containing regulatory sequences such as promoters, operators, repressors, enhancers, termination sequences, origins of replication, and other regulatory sequences that are compatible with the recombinant cell and that control the expression of nucleic acid molecules of the present invention. As used herein, a transcription control sequence- includes a sequence which is capable of controlling the initiation, elongation, and termination of transcription. Particularly important transcription control sequences are those which control transcription initiation, such as promoter, enhancer, operator and repressor sequences. Suitable transcription control sequences include any transcription control sequence that can function in at least one of the recombinant cells of the present invention. A variety of such transcription control sequences are known to those skilled in the art. Preferred transcription control sequences include those which function in bacterial, yeast, and mammalian cells, such as, but not limited to, tac, lac, trp, trc, oxy-pro, omp/lpp, rrnB, bacteriophage lambda (λ) (such as λp L and λp R and fusions that include such promoters), bacteriophage T7, T71aσ, bacteriophage T3, bacteriophage SP6, bacteriophage SP01, metallothionein, alpha mating factor, baculovirus, vaccinia virus, herpesvirus, poxvirus, adenovirus, simian virus 40, retrovirus actin, retroviral long terminal repeat, Rous sarcoma virus, heat shock, phosphate and nitrate transcription control sequences, as well as other sequences capable of controlling gene expression in prokaryotic or eukaryotic cells. Additional suitable transcription control sequences include tissue-specific promoters and enhancers as well as lymphokine-inducible promoters (e.g., promoters inducible by interferons or interleukins) . Transcription control sequences of the present invention can also include naturally occurring transcription control sequences naturally associated with a DNA sequence encoding an MEKK protein. Preferred nucleic acid molecules for insertion into an expression vector include nucleic acid molecules that encode at least a portion of an MEKK protein, or a homologue thereof. A more preferred nucleic acid molecule for insertion into an expression vector includes a nucleic acid molecule encoding at least a portion of an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and/or SEQ ID NO:10, or homologues thereof. An even more preferred nucleic acid molecule for insertion into an expression vector includes a nucleic acid molecule represented by SEQ ID N0:1, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and/or SEQ ID NO:9, or complements thereof. Expression vectors of the present invention may also contain fusion sequences which lead to the expression of inserted nucleic acid molecules of the present invention as fusion proteins. Inclusion of a fusion sequence as part of an MEKK nucleic acid molecule of the present invention can enhance the stability during production, storage and/or use of the protein encoded by the nucleic acid molecule. Furthermore, a fusion segment can function as a tool to simplify purification of an MEKK protein, such as to enable purification of the resultant fusion protein using affinity chromatography. A suitable fusion segment can be a domain of any size that has the desired function (e.g., increased stability and/or purification tool) . It is within the scope of the present invention to use one or more fusion segments. Fusion segments can be joined to amino and/or carboxy1 termini of an MEKK protein. Linkages between fusion segments and MEKK proteins can be constructed to be susceptible to cleavage to enable straight-forward recovery of the MEKK proteins. Fusion proteins are preferably produced by culturing a recombinant cell transformed with a fusion nucleic acid sequence that encodes a protein including the fusion segment attached to either the carboxy1 and/or amino terminal end of an MEKK protein. A recombinant cell of the present invention includes any cells transformed with at least one of any nucleic acid molecule of the present invention. A preferred recombinant cell is a cell transformed with at least one nucleic acid molecule that encodes at least a portion of an MEKK protein, or a homologue thereof. A more preferred recombinant cell is transformed with at least one nucleic acid molecule that is capable of encoding at least a portion of an amino acid sequence represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6 SEQ ID NO:8 and/or SEQ ID NO:10, or homologues thereof. An even more preferred recombinant cell is transformed with at least one nucleic acid molecule represented by SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and/or SEQ ID NO:9, or complements thereof. Particularly preferred recombinant cells include mammalian cells involved in a disease transformed with at least one of the aforementioned nucleic acid molecules. It may be appreciated by one skilled in the art that use of recombinant DNA technologies can improve expression of transformed nucleic acid molecules by manipulating, for example, the number of copies of the nucleic acid molecules within a host cell, the efficiency with which those nucleic acid molecules are transcribed, the efficiency with which the resultant transcripts are translated, and the efficiency of post-translational modifications. Recombinant techniques useful for increasing the expression of nucleic acid molecules of the present invention include, but are not limited to, operatively linking nucleic acid molecules to high-copy number plasmids, integration of the nucleic acid molecules into one or more host cell chromosomes, addition of vector stability sequences to plasmids, substitutions or modifications of transcription control signals (e.g., promoters, operators, enhancers). substitutions or modifications of translational control signals (e.g., ribosome binding sites, Shine-Dalgarno sequences) , modification of nucleic acid molecules of the present invention to correspond to the codon usage of the host cell, deletion of sequences that destabilize transcripts, and use of control signals that temporally separate recombinant cell growth from recombinant protein production during fermentation. The activity of an expressed recombinant protein of the present invention may be improved by fragmenting, modifying, or derivatizing the resultant protein. As used herein, amplifying the copy number of a nucleic acid sequence in a cell can be accomplished either by increasing the copy number of the nucleic acid sequence in the cell's genome or by introducing additional copies of the nucleic acid sequence into the cell by transformation. Copy number amplification is conducted in a manner such that greater amounts of enzyme are produced, leading to enhanced conversion of substrate to product. For example, recombinant molecules containing nucleic acids of the present invention can be transformed into cells to enhance enzyme synthesis. Transformation can be accomplished using any process by which nucleic acid sequences are inserted into a cell. Prior to transformation, the nucleic acid sequence on the recombinant molecule can be manipulated to encode an enzyme having a higher specific activity. In accordance with the present invention, recombinant cells can be used to produce an MEKK protein of the present invention by culturing such cells under conditions effective to produce such a protein, and recovering the protein. Effective conditions to produce a protein include, but are not limited to, appropriate media, bioreactor, temperature, pH and oxygen conditions that permit protein production. An appropriate, or effective, medium refers to any medium in which a cell of the present invention, when cultured, is capable of producing an MEKK protein. Such a medium is typically an aqueous medium comprising assimilable carbohydrate, nitrogen and phosphate sources, as well as appropriate salts, minerals, metals and other nutrients, such as vitamins. The medium may comprise complex nutrients or may be a defined minimal medium. Cells of the present invention can be cultured in conventional fermentation bioreactors, which include, but are not limited to, batch, fed-batch, cell recycle, and continuous fermentors. Culturing can also be conducted in shake flasks, test tubes, microtiter dishes, and petri plates. Culturing is carried out at a temperature, pH and oxygen content appropriate for the recombinant cell. Such culturing conditions are well within the expertise of one of ordinary skill in the art. Depending on the vector and host system used for production, resultant MEKK proteins may either remain within the recombinant cell or be secreted into the fermentation medium. The phrase "recovering the protein" refers simply to collecting the whole fermentation medium containing the protein and need not imply additional steps of separation or purification. MEKK proteins of the present invention can be purified using a variety of standard protein purification techniques, such as, but not limited to, affinity chromatography, ion exchange chromatography, filtration, electrophoresis, hydrophobic interaction chromatography, gel filtration chromatography, reverse phase chromatography, chromatofocusing and differential solubilization. In addition, an MEKK protein of the present invention can be produced by isolating the MEKK protein from cells expressing the MEKK protein recovered from an animal. For example, a cell type, such as T cells, can be isolated from the thymus of an animal. MEKK protein can then be isolated from the isolated T cells using standard techniques described herein. The present invention also includes a method to identify compounds capable of regulating signals initiated from a receptor on the surface of a cell, such signal regulation involving in some respect, MEKK protein. Such a method comprises the steps of: (a) contacting a cell containing an MEKK protein with a putative regulatory compound; (b) contacting the cell with a ligand capable of binding to a receptor on the surface of the cell; and (c) assessing the ability of the putative regulatory compound to regulate cellular signals by determining activation of a member of an MEKK-dependent pathway of the present invention. A preferred method to perform step (c) comprises measuring the phosphorylation of a member of an MEKK-dependent pathway. Such measurements can be performed using immunoassays having antibodies specific for phosphotyrosines, phosphoserines and/or phosphothreonines. Another preferred method to perform step (c) comprises measuring the ability of the MEKK protein to phosphorylate MEK protein and/or JEK protein using methods described herein. In another embodiment, a method to identify compounds capable of regulating signal transduction in a cell can comprise the steps of: (a) contacting a putative inhibitory compound with an MEKK protein to form a reaction mixture; (b) contacting the reaction mixture with MEK protein; and (c) assessing the ability of the putative inhibitory compound to inhibit phosphorylation of the MEK protein by the MEKK protein. The results obtained from step (c) can be compared with the ability of a putative inhibitory compound to inhibit the ability of Raf protein to phosphorylate MEK protein, to determine if the compound can selectively regulate signal transduction involving MEKK protein independent of Raf protein. MEKK, MEK and Raf proteins used in the foregoing methods can be recombinant proteins or naturally-derived proteins. Moreover, one can determine whether the site of inhibitory action along a particular signal transduction pathway involves both Raf and MEKK proteins by carrying out experiments set forth above (i.e., see discussion on MEKK- dependent pathways) . Another aspect of the present invention includes a kit to identify compounds capable of regulating signals initiated from a receptor on the surface of a cell, such signals involving in some respect, MEKK protein. Such kits include: (a) at least one cell containing MEKK protein; (b) a ligand capable of binding to a receptor on the surface of the cell; and (c) a means for assessing the ability of a putative regulatory compound to alter phosphorylation of the MEKK protein. Such a means for detecting phosphorylation include methods and reagents known to those of skill in the art, for example, phosphorylation can be detected using antibodies specific for phosphorylated amino acid residues, such as tyrosine, serine and threonine. Using such a kit, one is capable of determining, with a fair degree of specificity, the location along a signal transduction pathway of particular pathway constituents, as well as the identity of the constituents involved in such pathway, at or near the site of regulation. In another embodiment, a kit of the present invention can includes: (a) MEKK protein; (b) MEK protein; and (c) a means for assessing the ability of a putative inhibitory compound to inhibit phosphorylation of the MEK protein by the MEKK protein. A kit of the present invention can further comprise Raf protein and a means for detecting the ability of a putative inhibitory compound to inhibit the ability of Raf protein to phosphorylate the MEK protein. Another aspect of the present invention relates to the treatment of an animal having a medical disorder that is subject to regulation or cure by manipulating a signal transduction pathway in a cell involved in the disorder. Such medical disorders include disorders which result from abnormal cellular growth or abnormal production of secreted cellular products. In particular, such medical disorders include, but are not limited to, cancer, autoimmune disease, inflammatory responses, allergic responses and neuronal disorders, such as Parkinson's disease and Alzheimer's disease. Preferred cancers subject to treatment using a method of the present invention include, but are not limited to, small cell carcinomas, non-small cell lung carcinomas with overexpressed EGF receptors, breast cancers with overexpressed EGF or Neu receptors, tumors having overexpressed growth factor receptors of established autocrine loops and tumors having overexpressed growth factor receptors of established paracrine loops. According to the present invention, the term treatment can refer to the regulation of the progression of a medical disorder or the complete removal of a medical disorder (e.g., cure). Treatment of a medical disorder can comprise regulating the signal transduction activity of a cell in such a manner that a cell involved in the medical disorder no longer responds to extracellular stimuli (e.g., growth factors or cytokines) , or the killing of a cell involved in the medical disorder through cellular apoptosis. One aspect of the present invention involves the recognition that an MEKK protein of the present invention is capable of regulating the homeostasis of a cell by regulating cellular activity such as cell growth cell death, and cell function (e.g., secretion of cellular products) . Such regulation, in most cases, is independent of Raf, however, as discussed above (and as shown in Fig. 2) , some pathways capable of regulation by MEKK protein may be subject to upstream regulation by Raf protein. Therefore, it is within the scope of the present invention to either stimulate or inhibit the activity of Raf protein and/or MEKK protein to achieve desired regulatory results. Without being bound by theory, it is believed that the regulation of Raf protein and MEKK protein activity at the divergence point from Ras protein (see Fig. 2) can be controlled by a "2-hit" mechanism. For example, a first "hit" can comprise any means of stimulating Ras protein, thereby stimulating a Ras-dependent pathway, including, for example, contacting a cell with a growth factor which is capable of binding to a cell surface receptor in such a manner that Ras protein is activated. Following activation of Ras protein, a second "hit" can be delivered that is capable of increasing the activity of JNK activity compared with MAPK activity, or vice versa. A second "hit" can include, but is not limited to, regulation of JNK or MAPK activity by compounds capable of stimulating or inhibiting the activity of MEKK, JEK, Raf and/or MEK. For example, compounds such as protein kinase C or phospholipase C kinase, can provide the second "hit" needed to drive the divergent Ras-dependent pathway down the MEKK-dependent pathway in such a manner that JNK is preferentially activated over MAPK. One embodiment of the present invention comprises a method for regulating the homeostasis of a cell comprising regulating the activity of an MEKK-dependent pathway relative to the activity of a Raf-dependent pathway in the cell. As used herein, the term "homeostasis" refers to the tendency of a cell to maintain a normal state using intracellular systems such as signal transduction pathways. Regulation of the activity of an MEKK-dependent pathway includes increasing the activity of an MEKK-dependent pathway relative to the activity of a Raf-dependent pathway by regulating the activity of a member of an MEKK-dependent pathway, a member of a Raf-dependent pathway, and combinations thereof, to achieve desired regulation of phosphorylation along a given pathway, and thus effect apoptosis. Preferred regulated members of an MEKK- dependent pathway or a Raf-dependent pathway to regulate include, but are not limited to, proteins including MEKK, Raf, JEK, MEK, MAPK, JNK, TCF, ATF-2, Jun and Myc, and combinations thereof. In one embodiment, the activity of a member of an MEKK-dependent pathway, a member of a Raf-dependent pathway, and combinations thereof, are regulated by altering the concentration of such members in a cell. One preferred regulation scheme involves altering the concentration of proteins including MEKK, Raf, JEK, MEK, MAPK, JNK, TCF, Jun, ATF-2, and Myc, and combinations thereof. A more preferred regulation scheme involves increasing the concentration of proteins including MEKK, JEK, JNK, Jun, ATF-2, and Myc, and combinations thereof. Another more preferred regulation scheme involves decreasing the concentration of proteins including Raf, MEK, MAPK, and TCF, and combinations thereof. It is also within the scope of the present invention that the regulation of protein concentrations in two or more of the foregoing regulation schemes can be combined to achieve an optimal apoptotic effect in a cell. A preferred method for increasing the concentration of a protein in a regulation scheme of the present invention includes, but is not limited to, increasing the copy number of a nucleic acid sequence encoding such protein within a cell, improving the efficiency with which the nucleic acid sequence encoding such protein is transcribed within a cell, improving the efficiency with which a transcript is translated into such a protein, improving the efficiency of post-translational modification of such protein, contacting cells capable of producing such protein with anti-sense nucleic acid sequences, and combinations thereof. In a preferred embodiment of the present invention, the homeostasis of a cell is controlled by regulating the apoptosis of a cell. A suitable method for regulating the apoptosis of a cell is to regulate the activity of an MEKK- dependent pathway in which the MEKK protein regulates the pathway substantially independent of Raf. A particularly preferred method for regulating the apoptosis of a cell comprises increasing the concentration of MEKK protein by contacting a cell with a nucleic acid molecule encoding an MEKK protein that possesses unregulated kinase activity. A preferred nucleic acid molecule with which to contact a cell includes a nucleic acid molecule encoding an MEKK protein represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10, and combinations thereof. A more preferred nucleic acid molecule with which to contact a cell includes a nucleic acid molecule encoding a truncated MEKK protein having only the kinase catalytic domain (i.e., no regulatory domain) of an MEKK protein represented by SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and/or SEQ ID NO:10. An even more preferred nucleic acid molecule with which to contact a cell includes a nucleic acid molecule including MEKK1 352 . 672 , MEKK2 352 . 619 , MEKK3 358 . 626 , MEKK4 811 . 1195 , EKKδ^ j .^^, and combinations thereof. Again, suitable variations of MEKK proteins described herein comprise those proteins encoded by a nucleic acid molecule that are able to hybridize to any of the above sequences under stringent conditions. It is within the scope of the invention that the foregoing method can further comprise the step of decreasing the activity of MEK protein in the cell by contacting the cell with a compound capable of inhibiting MEK activity. Such compounds can include: peptides capable of binding to the kinase domain of MEK in such a manner that phosphorylation of MAPK protein by the MEK protein is inhibited; and/or peptides capable of binding to a portion of a MAPK protein in such a manner that phosphorylation of the MAPK protein is inhibited. In another embodiment, the activity of a member of an MEKK-dependent pathway, a member of a Raf-dependent pathway, and combinations thereof, can be regulated by directly altering the activity of such members in a cell. A preferred method for altering the activity of a member of an MEKK-dependent pathway, includes, but is not limited to, contacting a cell with a compound capable of directly interacting with a protein including MEKK, JEK, JNK, Jun, ATF-2, and Myc, and combinations thereof, in such a manner that the proteins are activated; and/or contacting a cell with a compound capable of directly interacting with a protein including Raf, MEK, MAPK, TCF protein, and combinations thereof in such a manner that the activity of the proteins are inhibited. A preferred compound with which to contact a cell that is capable of regulating a member of an MEKK-dependent pathway includes a peptide capable of binding to the regulatory domain of proteins including MEKK, JEK, JNK, Jun, ATF-2, and Myc, in which the peptide inhibits the ability of the regulatory domain to regulate the activity of the kinase domains of such proteins. Another preferred compound with which to contact a cell includes TNFα, growth factors regulating tyrosine kinases, hormones regulating G protein-coupled receptors and FAS ligand. A preferred compound with which to contact a cell that is capable of regulating a member of a Raf-dependent pathway includes a peptide capable of binding to the kinase catalytic domain of a protein selected from the group consisting of Raf, MEK-1, MEK-2, MAPK, and TCF, in which the peptide inhibits the ability of the protein to be phosphorylated or to phosphorylate a substrate. One aspect of the present invention relates to the recognition that an MEKK protein is capable of activating MAPK. MAPK is known to be involved in various cellular pathways in mammalian systems. MAPK is known to be involved in cellular mitogenesis, DNA synthesis, cell division and differentiation. MAPK is also recognized as being involved in the activation of oncogenes, such as c- jun and c-myc. While not bound by theory, the present inventor believes that MAPK is also intimately involved in various abnormalities having a genetic origin. MAPK is known to cross the nuclear membrane and is believed to be at least partially responsible for regulating the expression of various genes. As such, MAPK is believed to play a significant role in the instigation or progression of cancer, neuronal diseases, autoimmune diseases, allergic reactions, wound healing and inflammatory responses. The present inventor, by being first to identify nucleic acid sequences encoding MEKK, recognized that it is now possible to regulate the expression of MEKK, and thus regulate the activation of MAPK. The present invention also includes a method for regulating the homeostasis of a cell comprising injecting an area of a subject's body with an effective amount of a naked plasmid DNA compound. A naked plasmid DNA compound comprises a nucleic acid molecule encoding an MEKK protein of the present invention, operatively linked to a naked plasmid DNA vector capable of being taken up by and expressed in a recipient cell located in the body area. A preferred naked plasmid DNA compound of the present invention comprises a nucleic acid molecule encoding a truncated MEKK protein having deregulated kinase activity. Preferred naked plasmid DNA vectors of the present invention include those known in the art. When administered to a subject, a naked plasmid DNA compound of the present invention transforms cells within the subject and directs the production of at least a portion of an MEKK protein or RNA nucleic acid molecule that is capable of regulating the apoptosis of the cell. A naked plasmid DNA compound of the present invention is capable of treating a subject suffering from a medical disorder including cancer, autoimmune disease, inflammatory responses, allergic responses and neuronal disorders, such as Parkinson's disease and Alzheimer's disease. For example, a naked plasmid DNA compound can be administered as an anti-tumor therapy by injecting an effective amount of the plasmid directly into a tumor so that the plasmid is taken up and expressed by a tumor cell, thereby killing the tumor cell. As used herein, an effective amount of a naked plasmid DNA to administer to a subject comprises an amount needed to regulate or cure a medical disorder the naked plasmid DNA is intended to treat, such mode of administration, number of doses and frequency of dose capable of being decided upon, in any given situation, by one of skill in the art without resorting to undue experimentation. Therapeutic compounds for use with a treatment method of the present invention can further comprise suitable excipients. A therapeutic compound for use with a treatment method of the present invention can be formulated in an excipient that the subject to be treated can tolerate. Examples of such excipients include water, saline. Ringer's solution, dextrose solution. Hank's solution, and other aqueous physiologically balanced salt solutions. Nonaqueous vehicles, such as fixed oils, sesame oil, ethyl oleate, or triglycerides may also be used. Other useful excipients include suspensions containing viscosity enhancing agents, such as sodium carboxymethylcellulose, sorbitol, or dextran. Excipients can also contain minor amounts of additives, such as substances that enhance isotonicity and chemical stability. Examples of buffers include phosphate buffer, bicarbonate buffer and Tris buffer, while examples of preservatives include thimerosal, m- or o-cresol, formalin and benzyl alcohol. Standard formulations can either be liquid injectables or solids which can be taken up in a suitable liquid as a suspension or solution for injection. Thus, in a non-liquid formulation, the excipient can comprise dextrose, human serum albumin, preservatives, etc., to which sterile water or saline can be added prior to administration. In another embodiment, a therapeutic compound for use with a treatment method of the present invention can also comprise a carrier. Carriers are typically compounds that increase the half-life of a therapeutic compound in the treated animal. Suitable carriers include, but are not limited to, liposomes, micelles, cells, polymeric controlled release formulations, biodegradable implants, bacteria, viruses, oils, esters, and glycols. Preferred carriers include liposomes and micelles. A therapeutic compound for use with a treatment method of the present invention can be administered to any subject having a medical disorder as herein described. Acceptable protocols by which to administer therapeutic compounds of the present invention in an effective manner can vary according to individual dose size, number of doses, frequency of dose administration, and mode of administration. Determination of such protocols can be accomplished by those skilled in the art without resorting to undue experimentation. An effective dose refers to a dose capable of treating a subject for a medical disorder as described herein. Effective doses can vary depending upon, for example, the therapeutic compound used, the medical disorder being treated, and the size and type of the recipient animal. Effective doses to treat a subject include doses administered over time that are capable of regulating the activity, including growth, of cells involved in a medical disorder. For example, a first dose of a naked plasmid DNA compound of the present invention can comprise an amount of that causes a tumor to decrease in size by about 10% over 7 days when administered to a subject having a tumor. A second dose can comprise at least the same the same therapeutic compound than the first dose. Another aspect of the present invention includes a method for prescribing treatment for subjects having a medical disorder as described herein. A preferred method for prescribing treatment comprises: (a) measuring the MEKK protein activity in a cell involved in the medical disorder to determine if the cell is susceptible to treatment using a method of the present invention; and (b) prescribing treatment comprising regulating the activity of an MEKK- dependent pathway relative to the activity of a Raf- dependent pathway in the cell to induce the apoptosis of the cell. The step of measuring MEKK protein activity can comprise: (1) removing a sample of cells from a subject; (2) stimulating the cells with a TNFα; and (3) detecting the state of phosphorylation of JEK protein using an immunoassay using antibodies specific for phosphothreonine and/or phosphoserine. The present invention also includes antibodies capable of selectively binding to an MEKK protein of the present invention. Such an antibody is herein referred to as an anti-MEKK antibody. Polyclonal populations of anti-MEKK antibodies can be contained in an MEKK antiserum. MEKK antiserum can refer to affinity purified polyclonal antibodies, ammonium sulfate cut antiserum or whole antiserum. As used herein, the term "selectively binds to" refers to the ability of such an antibody to preferentially bind to MEKK proteins. Binding can be measured using a variety of methods known to those skilled in the art including immunoblot assays, immunoprecipitation assays, enzyme immunoassays (e.g., ELISA), radioimmunoassays, immunofluorescent antibody assays and immunoelectron microscopy; see, for example, Sambrook et al.. Molecular Cloning: A Laboratory Manual , Cold Spring Harbor Labs Press, 1989. Antibodies of the present invention can be either polyclonal or monoclonal antibodies and can be prepared using techniques standard in the art. Antibodies of the present invention include functional equivalents such as antibody fragments and genetically-engineered antibodies, including single chain antibodies, that are capable of selectively binding to at least one of the epitopes of the protein used to obtain the antibodies. Preferably, antibodies are raised in response to proteins that are encoded, at least in part, by a MEKK nucleic acid molecule. More preferably antibodies are raised in response to at least a portion of an MEKK protein, and even more preferably antibodies are raised in response to either the amino terminus or the carboxyl terminus of an MEKK protein. Preferably, an antibody of the present invention has a single site binding affinity of from about lO^ "1 to about 10 12 M "1 for an MEKK protein of the present invention. A preferred method to produce antibodies of the present invention includes administering to an animal an effective amount of an MEKK protein to produce the antibody and recovering the antibodies. Antibodies of the present invention have a variety of potential uses that are within the scope of the present invention. For example, such antibodies can be used to identify unique MEKK proteins and recover MEKK proteins. Another aspect of the present invention comprises a therapeutic compound capable of regulating the activity of an MEKK-dependent pathway in a cell identified by a process, comprising: (a) contacting a cell with a putative regulatory molecule; and (b) determining the ability of the putative regulatory compound to regulate the activity of an MEKK-dependent pathway in the cell by measuring the activation of at least one member of said MEKK-dependent pathway. Preferred methods to measure the activation of a member of an MEKK-dependent pathway include measuring the transcription regulation activity of c-Myc protein, measuring the phosphorylation of a protein selected from the group consisting of MEKK, JEK, JNK, Jun, ATF-2, Myc, and combinations thereof. The following examples are provided for the purposes of illustration and are not intended to limit the scope of the present invention. EXAMPLES Example 1 This example describes the structural characterization of MEKK l protein. A. MEKK 1 Nucleotide Sequence MEKK 1 protein was cloned by the following method. Unique degenerate inosine oligodeoxynucleotides were designed to correspond to regions of sequence identity between the yeast Stell and Byr2 genes. With primers and cDNA templates derived from polyadenylated RNA from NIH 3T3 cells, a polymerase chain reaction (PCR) amplification product of 320 base pairs (bp) was isolated. This 320 bp cDNA was used as a probe to identify an MEKK 1 cDNA of 3260 bp from a mouse brain cDNA library using standard methods in the art. The MEKK 1 nucleotide sequence was determined by dideoxynucleotide sequencing of double-stranded DNA using standard methods in the art. Referring to Table 6, based on the Kozak consensus sequence for initiation codons, the starting methionine can be predicted to occur at nucleotide 486. With this methionine at the start, the cDNA encodes a protein of 672 amino acids, corresponding to a molecular size of 73 kD. There is another in-frame methionine at position 441, which does not follow the Kozak rule, but would yield a protein of 687 amino acid residues (74.6 kD) . Also referring to Table 6, 20% of the NH 2 -terminal 400 amino acids are serine or threonine and there are only two tyrosines. Several potential sites of phosphorylation by protein kinase C are apparent in the NH 2 -terminal region. The kinase catalytic domain is located in the COOH-terminal half of the MEKK 1. B. Southern Blot Analysis of MEKK 1 Transcript Equal amounts (20 μg) of total RNA were loaded onto the gel as indicated by ethidium bromide staining. Blots were probed with either a 320-bp cDNA fragment encoding a portion of the MEKK kinase domain or an 858-bp fragment encoding a portion of the NH 2 terminal region of MEKK using standard methods in the art. Referring to Fig. 3A, a 7.8 kb mRNA was identified with probes derived from both the 5' and 3' ends of the MEKK cDNA in several cell lines and mouse tissues. The MEKK mRNA was highly expressed in mouse heart and spleen, an in lower amounts in liver. C. Southern Blot Analysis Mouse genomic DNA (10 μg) was digested with either Bain HI, Hind III or Eco RI and applied to gels using standard methods in the art. Blots were probed with a 320-bp fragment of the MEKK gene. Fig. 3B shows the appearance of one band in the Bam HI and Hind III digests which indicates that MEKK is encoded by one gene. The appearance of two bands in the Eco RI digest indicates the likely presence of an Eco RI site within an intron sequence spanned by the probe. D. Immunoblots Using Anti-MEKK Antibodies Three polyclonal antisera were prepared using three different antigens. A first polyclonal antiserum was prepared using an antigen comprising a 15 amino acid peptide DRPPSRELLKHPVER derived from the COOH-terminus of MEKK. NZW rabbits were immunized with the peptide and antisera was recovered using standard methods known in the art. This first polyclonal antiserum is hereinafter referred to as the DRPP antiserum. A second polyclonal antiserum was produced using a DNA clone comprising an MEKK cDNA digested with EcoRl and Pstl, thereby creating a 1270 bp fragment that encodes the amino terminus of MEKK. This fragment was cloned into pRSETC to form the recombinant molecule pMEKK.,_ 369 comprising amino acid residues 1 to 369 of MEKK 1. The pMEKKl,. 369 recombinant molecule was expressed in E. coli and protein encoded by the recombinant molecule was recovered and purified using standard methods known in the art. NZW rabbits were immunized with the purified recombinant MEKKl,,. 369 protein and antisera was recovered using standard methods known in the art. This second polyclonal antiserum is hereinafter referred to as the MEKKl.,.^ antiserum. A third polyclonal antiserum was produced using a DNA clone comprising an MEKK cDNA digested with Pst I and Kpn 1 , thereby creating a 1670 bp fragment that encodes the catalytic domain of MEKK. This fragment was cloned into pRSETC to form the recombinant molecule pMEKK^ Q .-^ g comprising amino acid residues 370 to 738 of MEKK 1 (encoded by base pairs 1592-3260) . The pMEKKl^ Q .^ g recombinant molecule was expressed in E. coli and protein encoded by the recombinant molecule was recovered and purified using standard methods known in the art. NZW rabbits were immunized with the purified recombinant MEKKl^ Q .^ g protein and antisera was recovered using standard methods known in the art. This second polyclonal antiserum is hereinafter referred to as the MEKKl- j -,,,..^ antiserum. The DRPP antiserum was used to probe Western Blots of soluble cellular protein derived from several rodent cell lines. Soluble cellular protein (100 μg) or recombinant MEKK COOH-terminal fusion protein (30 ng) was loaded onto a 10% Tris Glycine SDS-PAGE gel and the protein transferred to a nylon filter using methods standard in the art. The nylon filter was immunoblotted with affinity purified DRPP antiserum (1:300 dilution). Referring to Fig. 3C, a 78 kD immunoreactive protein was identified in the samples comprising protein from Pheochromocytoma (PC12) , Rat la, and NIH 3T3 cells. A prominent 50 kD immunoreactive band was also commonly present but varied in intensity from preparation to preparation indicating the band is a proteolytic fragment. Visualization of both the 78 kD and 50 kD immunoreactive bands on immunoblots was inhibited by pre-incubation of the 15 amino acid peptide antigen with the affinity purified DRPP antiserum. The MEKK protein detected by immunoblotting is similar to the molecular size predicted from the open reading frame of the MEKK cDNA. In a second immunoblot experiment, PC12 cells stimulated or not stimulated with EGF were lysed and resolved on 10% Tris Glycine SDS-PAGE gel as described above. MEKK proteins contained in the cell lysates were identified by immunoblot using affinity purified MEKK1_,. 369 antiserum (1:300) using methods standard in the art. Referring to Fig. 4, MEKK 1 and two higher molecular weight proteins having MEKK activity, MEKK a and MEKK β, were identified using the affinity purified MEKK1_,_ 369 antiserum. MEKK 1, and not MEKK and MEKK β, were identified using the affinity purified MEKK1 1 „ 369 antiserum. Using the same procedure described above, two MEKK immunoreactive species of approximately 98 kD and 82 kD present in PC12, Ratla, NIH3T3, and Swiss3T3 cell lysates were recognized by affinity purified MEKK1_,_ 369 antiserum as shown in Fig. 5. It should be noted that the 98 kD MEKK protein described herein was originally identified as a 95 kD MEKK protein in the related PCT application (International application no. PCT/US94/04178) . Subsequent Tris Glycine SDS-PAGE gel analysis has led to the determination that the modification in molecular weight. Visualization of both of these proteins was inhibited by incubation of the affinity purified MEKK1_,. 369 antiserum with purified recombinant MEKKl,.^ fusion protein antigen. A single 98 kD MEKK protein was present in MEKK immunoprecipitates, but not in immunoprecipitates using preimmune serum. More of the 98 kD MEKK was expressed in PC12 cells relative to fibroblast cell lines. Immunoblotting with antibodies that specifically recognize Raf-1 or Raf-B indicated that neither of these enzymes were present as contaminants of MEKK immunoprecipitates. 98 kD MEKK in MEKK immunoprecipitates did not comigrate with Raf- 1 or Raf-B in PC12 cell lysates and no cross-reactivity between MEKK and Raf antibodies was observed. Example 2 This example describes the isolation of nucleic acid sequences encoding MEKK 2, MEKK 3 and MEKK 4 protein. PCR primers were designed based on the nucleotide sequence of MEKK 1. PCR amplification of fragments from DNA isolated from reverse transcriptase reactions of RNA isolated form PC12 and HL60 cells was conducted using standard techniques. The resultant PCR products were cloned into the pGEX cloning vector (Promega, Wisconsin) using standard procedures and submitted to DNA sequence analysis using standard techniques. Example 3 This example describes the expression of MEKK 1 protein in COS-1 cells to define its function in regulating the signaling system that includes MAPK. COS cells in 100-mm culture dishes were transfected with either the pCVMV5 expression vector alone (1 μg: control) or the pCVMV5 MEKK construct (1 μg: MEKK) . After 48 hours, the cells were placed in serum-free medium containing bovine serum albumin (0.1 percent) for 16 to 18 hours to induce quiescence. Cells were then treated with human EGF (30 ng/ml) (+EGF) or buffer (control) for 10 minutes, washed twice in cold phosphate buffered saline (PBS) , and lysed in cell lysis buffer containing 50 mM β- glycerophosphate (pH 7.2), 100 μM sodium vanadate, 2 mM MgCl 2 , ImM EGTA Triton X-100 (0.5 percent), leupeptin (2 μg/ml) , aprotinin (2μg/ml) , and 1 mM dithiothreitol (600 μl) . After centrifugation for 10 minutes at maximum speed in a microfuge, COS cell lysates containing 0.5 to 1 mg of soluble protein were subjected to FPLC on a MONO Q column, and eluted fractions were assayed for MAPK activity according to the method described in Heasley et al., p. 545, 1992, Mol . Biol. Cell , Vol. 3. Referring to Fig. 6A, when MEKK 1 was overexpressed in COS 1 cells, MAPK activity was four to five times greater than that in control cells transfected with plasmid lacking an MEKK 1 cDNA insert. The activation of MAPK occurred in COS cells deprived of serum and in the absence of any added growth factor. The activity of MAPK was similar to that observed after stimulation of control cells with EGF. Stimulation of COS cells transiently overexpressing MEKK with EGF resulted in only a slight increase in MAPK activity compared to that observed with MEKK expression alone. To ensure that MEKK protein was present in the samples tested for MAPK activity, protein from cell lysates of the transfected COS 1 cells were immunoblotted with MEKK specific antiserum. Equal amounts (100 μg) of soluble protein lysate from COS cells were placed on the gel for immunoblotting using the methods described in Example 1. The filters were immunoblotted using the affinity purified DRPP antiserum (1:300) and affinity purified MEKK.,_ 369 antiserum (1:300). Referring to Fig. 6B, the results indicate that expression of MEKK in cells transfected with vector encoding MEKK that were treated with or without EGF. Only the 50 kD MEKK immunoreactive fragment was detected in lysates from control COS cells using the DRPP antiserum. Transient expression of MEKK in COS cells yielded a predominant 82 kD band that was slightly larger than that observed in PC12, Rat la, or NIH 3T3 cells. Addition of the 15 amino acid DRPP peptide antigen to the antiserum during immunoblotting prevented detection of all of the immunoreactive bands; these bands were not detected in extracts of control COS cells, an indication that they were derived from the expressed MEKK protein. Example 4 This Example describes the expression of MEKK 1 in COS cells to test the ability of MEKK protein to activate MEK protein. Recombinant MAPK was used to assay MEK activity in COS cell lysates that had been fractionated by fast protein liquid chromatography (FPLC) on a Mono S column. A cDNA encoding p42 MAPK from Xenopus laevis was cloned into the pRSETB expression vector. This construct was used for expression in the LysS strain of Escherichia coli BL21(DE3) of a p42 MAPK fusion protein containing a polyhistidine sequence at the NH 2 -terminus. Cultures containing the expression plasmid were grown at 37°C to an optical density of 0.7 to 0.9 at 600 nM. Isopropyl-β-thiogalactopyranoside (0.5 mM) was added to induce fusion protein synthesis and the cultures were incubated for 3 hours. The cells were then collected and lysed by freezing, thawing, and sonication. The lysate was centrifuged at 10,000g for 15 minutes at 4°C. The supernatant was then passed over a Ni 2+" charged Sepharose resin and the soluble recombinant MAPK was eluted in sodium phosphate buffer (pH 4.5). The purified recombinant MAPK was more than 80 percent pure. The purified recombinant MAPK served as a substrate for MEK and catalyzed the phosphorylation of a peptide consisting of residues 662 to 681 of the EGF receptor (EGFR 662"681 ) . Soluble cell lysates from COS cells transiently transfected with MEKK, mock-transfected (control) , or mock- transfected and treated with EGF (30 ng/ml) (+EGF) , were fractionated by FPLC on a Mono s column and endogenous MEK activity was measured. Endogenous MAPK eluted in fractions 2 to 4, whereas MEK was contained in fractions 9 to 13. For assaying endogenous MEK activity, cells were washed twice in cold PBS and lysed in 650 μl of a solution containing 50 mM β-glycerophosphate, 10 mM 2-N- morpholinoethane-sulfonic acid (pH 6.0), 100 μM sodium vanadate, 2 mM MgCl 2 , 1 mM EGTA, Triton X-100 (0.5 percent) , leupeptin (5 μg/ml) , aprotinin (2 μg/ml) , and 1 mM dithiothreitol. After centrifugation at maximum speed for 10 minutes in a microfuge, soluble cell lysates (1 to 2 mg of protein) were applied to a Mono S column equilibrated in elution buffer (50 mM β-glycerophosphate, 10 mM MES (pH 6.0) , 100 μM sodium vanadate, 2 mM MgCl 2 , 1 mM EGTA, and 1 mM dithiothreitol. The column was washed with buffer (2 ml) and bound proteins were eluted with a 30ml linear gradient of 0 to 350 mM NaCl in elution buffer. A portion (30 μl) of each fraction was assayed for MEK activity by mixing with buffer (25 mM β-glycerophosphate, 40 mM W-(2- hydroxyethyl)piperazine-N•-(2-ethanolsulfonicacid) (pH7.2) 50 mM sodium vanadate, 10 mM MgCl 2 , 100 μM γ- 32 P-ATP (3000 to 4000 cpm/pmol) , inhibitor protein-20 (IP-20; TTYADFIASGRTGRRNAIHD; 25 μg/ml), 0.5 mM EGTA, recombinant MAP kinase (7.5 μg/ml), and 200 μM EGFR 662"681 ) in a final volume of 40 μl. After incubation at 30°C for 20 minutes, the incorporation of γ- 3 P-ATP into EGFR 662"681 was measured. In this assay, the ability of each column fraction to activate added recombinant MAPK was measured by the incorporation of γ- 32 P-ATP into the MAPK substrate, a peptide derived from the EGF receptor (EGFR) . Referring to Fig. 7, the first peak of activity eluted represents endogenous activated MAPK, which directly phosphorylates the EGFR peptide substrate. The second peak of activity represents the endogenous MEK in COS cells. The activity of endogenous MEK activity was characterized by fractionation of Mono S FPLC. COS cell lysates were fractionated by FPLC on a Mono Q column to partially purify the expressed MEKK. Purified recombinant MEK-1 was then used as a substrate for MEKK in the presence of γ- 32 P-ATP to determine whether MEKK directly phosphorylates MEK-1. A cDNA encoding MEK-1 was obtained from mouse B cell cDNA templates with the polymerase chain reaction and oligodeoxynucleotide primers corresponding to portions of the 5' coding region and 3' untranslated region of MEK-1. The catalytically inactive MEK-1 was generated by site- directed mutagenesis of Lys 343 to Met. The wild-type MEK-1 and catalytically inactive MEK-1 proteins were expressed in pRSETA as recombinant fusion proteins containing a polyhistidine sequence at their NH 2 -termini. Lysates from COS cells transfected with MEKK or mock- transfected (control) were subjected to FPLC on a Mono Q column as described above. Portions (20 μl) of fractions containing MEKK were mixed with buffer containing 50 mM β- glycerophosphate (pH 7.2), 100 μM sodium vanadate, 2 mM MgCl 2 , ImM EGTA, 50 μM ATP, IP-20 (50 μg/ml) , and 10 μl γ- 32 P-ATP in a reaction volume of 40 μl and incubated for 40 minutes in the presence (+) or absence (-) of recombinant, catalytically inactive MEK-1 (150 ng) (kinase-MEK-1) . Reactions were stopped by the addition of 5 x SDS sample buffer (10 μl) , 1 x SDS buffer contains 2 percent SDS, 5 percent glycerol, 62.5 mM tris-HCl (pH 6.8), 5 percent β- mercaptoethanol, and 0.001 percent bromophenol blue. The samples were boiled for 3 minutes and subjected to SDS-PAGE and autoradiography. Referring to Fig. 8A, autophosphorylated recombinant wild-type MEK-1 (WT MEK-1) comigrated with phosphorylated catalytically inactive MEK-1. Thus, MEKK was capable of phosphorylating MEK-1. Corresponding fractions of lysates from control cells, however, were not able to phosphorylate MEK-1. Example 5 This example describes studies showing that the modified form of MEK-1 that was used in the phosphorylation assay of Example 4 did not autophosphorylate as does wild- type MEK-1. Phosphorylation of catalytically inactive MEK-1 by MEKK was time dependent (Fig. 8B) ; MEKK was also phosphorylated. Fraction 22 from FPLC on a Mono Q column (20 μl) was incubated with or without recombinant catalytically inactive MEK-1 (0.15 μg) for the indicated times. Referring to Fig. 8B, phosphorylation of kinase MEK-1 and MEKK was visable after 5 minutes and maximal after about 20 minutes. The time-dependent increase in MEKK phosphorylation correlated with a decreased mobility of the MEKK protein during SDS-PAGE. Referring to Fig. 8C, immunoblotting demonstrated that the MEKK protein co-eluted (after FPLC on a Mono Q column) with the peak of activity (fraction 22) that phosphorylated MEK. The slowly migrating species of MEKK were also detected by immunoblotting. Thus, expression of MEKK appears to activate MAPK by activating MEK. Example 6 This Example describes that the phosphorylation of MEK by overexpressed MEKK resulted in activation of MEK, recombinant wild-type MEK-1 and a modified form of MAPK that is catalytically inactive. COS cell lysates were separated by Mono Q-FPLC and fractions containing MEKK were assayed for their ability to activate added wild-type MEK-1 such that it would phosphorylate catalytically inactive recombinant MAPK in the presence of γ- 32 P-ATP. Lysates from COS cells transfected with MEKK or mock-transfeeted (control) were fractionated by FPLC on a Mono Q column and portions (20 μl) of fractions containing MEKK were mixed with buffer. Each fraction was incubated in the presence (+) or absence (-) of purified recombinant wild-type MEK-1 (150 ng) and in the presence of purified recombinant, catalytically inactive (kinase " ) MAPK (300 ng) . Referring to Fig. 9A, fractions 20 to 24 from lysates of COS cells transfected with MEKK activated MEK-1. Thus, MEKK phosphorylated and activated MEK-1, leading to MAPK phosphorylation. Example 7 This Example describes studies demonstrating that MEKK activated MEK directly, and not through the activation of one or more other kinases contained in the column fractions. Overexpressed MEKK was immunoprecipitated from COS cell lysates with affintiy purified MEKK 1 _ 369 antiserum. Immunoprecipitated MEKK was resuspended in 10 to 15 μl of PAN (10 mM piperazine-N, N'-bis-2-ethanesulfonic acid (Pipes) (pH 7.0), 100 mM NaCl, and aprotinin (20 μg/ml) and incubated with (+) or without (-) catalytically inactive MEK-1 (150 ng) and 25 μCi of γ- 32 P-ATP in 20 mM pipes (pH 7.0), 10 mM MnCl 2 , and aprotinin (20 μg/ml) in a final voume of 20 μl for 15 minutes 30°C. Reactions were stopped by the addition of 5 x SDS sample buffer (5 μl) . The samples were boiled for 3 minutes and subjected to SDS-PAGE and autoradiography. Referring to Fig. 9B, MEKK phosphorylated catalytically inactive MEK-1, which comigrated with wild- type MEK-1 on SDS-PAGE. Several phosphorylated bands of overexpressed MEKK were detected in the immunoprecipitates. These bands probably resulted from autophosphorylation of MEKK and corresponded to the forms of MEKK identified by immunoblotting of lysates from COS cells transfected with MEKK. Immunoprecipitates obtained with pre-immune serum contained no MEKK and did not phosphorylate MEK-1. Thus, MEKK appears to directly phosphorylate MEK. Taken together, the results from Examples 4 through 7 show that MEKK can phosphorylate and activate MEK, which in turn phosphorylates and activates MAPK. Example 8 This Example demonstrates that Raf can also phosphorylate and activate MEK. COS cells deprived of serum were stimulated with EGF, and Raf was immunoprecipitated with an antibody to the COOH-terminus of Raf-1. Cos cells were transiently transfected with vector alone (control) or with the PCV/M5- MEKK construct (MEKK) . Quiescent control cells were treated with or without human EGF (30 ng/ml) for 10 minutes and Raf was immunoprecipitatd from cell lysates with an antibody to a COOH-terminal peptide from Raf. Immunoprecipitated Raf was incubated with catalytically inactive MEK-1 (150 ng) and 25 μl of γ- 3 P-ATP. The immunoprecipitated Raf phosphorylated MEK-1 in the presence of γ- 32 P-ATP (Fig. 10A) . Little or no phosphorylation of MEK-1 by Raf was observed in immunoprecipitates of Raf from COS cells overexpressing MEKK. Treatment of COS cells overexpressing MEKK with EGF resulted in a similar degree of phosphorylation of MEK-1 by immunoprecipitated Raf (Fig. 10B) . Cells transfected with MEKK and deprived of serum were treated with EGF, and Raf was immunoprecipitated and incubated with catalytically inactive MEK-1. Equal amounts of Raf were immunoprecipitated in each sample as demonstrated by immunoblotting with antibodies to Raf. The slowest migrating band represents an immunoprecipitated phosphoprotein that is unrelated to Raf or MEK-1. The amount of Raf in the immunoprecipitates from control cells and cells transfected with MEKK was similar as shown by subsequent SDS-PAGE and immunoblotting with the antibody to Raf. Thus, both MEKK and Raf can independently activate MEK. Example 9 This Example describes the activation of a 98 kD MEKK protein isolated from PC12 cells in response to stimulation of cells containing MEKK protein by growth factors. PC12 cells were deprived of serum by incubation in starvation media (DMEM, 0.1% BSA) for 18-20 hours and MEKK was immunoprecipitated from lysates containing equal amounts of protein from untreated controls or cells treated with EGF (30ng/ml) or NGF (lOOng/ml) for 5 minutes with the above-described anti-MEKK antibodies speicific for the NH 4 - terminal portion of MEKK. Immunoprecipitated MEKK was resuspended in 8μl of PAN (lOmM piperazine-N,N'-bis-2- ethanesulfonic acid (Pipes) (pH 7.0), lOOmM NaCl, and aprotinin (20μg/ml)) and incubated with catalytically inactive MEK-1 (150ng) and 40μCi of (γ- 32 P)ATP in universal kinase buffer (20mM piperazine-N,N'-bis-2-ethanesulfonic acid (Pipes) (pH 7.0), lOmM MnCl 2 , and aprotinin (20μg/ml) ) in a final volume of 20μl for 25 minutes at 30°C. Reactions were stopped by the addition of 2X SDS sample buffer (20μl) . The samples were boiled for 3 minutes and subjected to SDS-PAGE and autoradiography. Raf-B was immunoprecipitated from the same untreated and treated PC12 cell lysates as above with an antiserum to a COOH-terminal peptide of Raf-B (Santa Cruz Biotechnology, Inc.) and assayed similarly. Raf-1 was immunoprecipitated with an antiserum to the 12 COOH-terminal amino acids of Raf-1 (Santa Cruz Biotechnology, Inc.). Epidermal growth factor (EGF) treatment of serum starved PC12 cells resulted in increased MEKK activity. Referring to Fig. 11, the results were obtained by measuring the phosphorylation of purified MEK-1 (a kinase inactive form) by immunoprecipitates of MEKK in in vitro kinase assays. NGF stimulated a slight increase in MEKK activity compared to control immunoprecipitates from untreated cells. Stimulation of MEKK activity by NGF and EGF was similar to Raf-B activation by these agents, although Raf-B exhibited a high basal activity. Activation of c-Raf-1 by NGF and EGF was almost negligible in comparison to that of MEKK or Raf-B. A timecourse of MEKK stimulation by EGF was established by immunoprecipitating MEKK or Raf-B protein from lysates of PC12 cells treated with EGF (30ng/ml) for 0, 1, 3, 5, 10, or 20 minutes and incubating the protein with catalytically inactive MEK-1 (150ng) and (γ- 32 P)ATP as described above. Data represent the relative magnitude of the response for each timepoint as quantitated by phosphorimager analysis of radioactive gels from a typical experiment. A timecourse of EGF treatment indicated that MEKK activation reached maximal levels following 5 minutes and persisted for at least 30 minutes (Fig. 12) . Raf-B exhibited a similar timecourse; peak activity occurred within 3-5 minutes following EGF treatment and was persistent for up to 20 minutes. To further dissociate EGF-stimulated MEKK activity from that of Raf-B, Raf-B was immunodepleted from cell lysates prior to MEKK immunoprecipitation. Raf-B was pre- cleared from lysates of serum-starved PC12 cells which had been either treated or not treated with EGF (30ng/ml) for 5 minutes. Raf-B was pre-cleared two times using antisera to Raf-B or using preimmune IgG antisera as a control. The pre-cleared supernatant was then immunoprecipitated with either MEKK or Raf-B antisera and incubated with catalytically inactive MEK-1 and (γ- 32 P)ATP as described in detail above. EGF-stimulated and unstimulated PC12 cell lysates were precleared with either IgG or Raf-B antisera and then subjected to immunoprecipitation with MEKK antiserum or Raf-B antibodies. The results shown in Fig. 13 indicate that pre-clearing with Raf-B resulted in a 60% diminution of Raf-B activity as measured by phosphorimager analysis of Raf-B in vitro kinase assays. EGF-stimulated MEKK activity was unaffected by Raf-B depletion, suggesting that Raf-B is not a component of MEKK immunoprecipitates. At least 40% of the Raf-B activity is resistant to preclearing with Raf-B antibodies. Recombinant wild type MEKK over-expressed in COS cells readily autophosphorylates on serine and threonine residues and the amino-terminus of MEKK is highly serine and threonine rich. MEKK contained in immunoprecipitates of PC12 cells were tested for selective phosphorylation of purified recombinant MEKK amino-terminal fusion protein in in vitro kinase assays. Serum-starved PC12 cells were treated with EGF (30ng/ml) for 5 minutes and equal amounts of protein from the same cell lysates were immunoprecipitated with either MEKK, Raf-B, or preimmune antiserum as a control. Immunoprecipitates were incubated with purified recombinant MEKK NH 2 -terminal fusion protein (400ng) and (γ- 32 P)ATP as described above. The results shown in Fig. 14 indicate that MEKK immunoprecipitated from lysates of EGF-stimulated and unstimulated PC12 cells robustly phosphorylated the inert 50 kD MEKK NH 2 -fusion protein, while Raf-B or preimmune immunoprecipitates from EGF-stimulated or unstimulated cells did not use the MEKK NH 2 -fusion protein as a substrate. Thus, the EGF-stimulated MEKK activity contained in MEKK immunoprecipites is not due to contaminating Raf kinases. Example 10 This Example describes MEKK activity in FPLC Mono Q ino-exchnage column fractions of PC12 cell lysates. Cell lysates were prepared from EGF-stimulated PC12 cells. Portions (900 μl) of 1 ml column fractions (1 to 525 mM NaCl gradient) were concentrated by precipitation with trichloroacetic acid and loaded on gels as described above. The gels were blotted and then immunoblotted with MEKK specific antibody. The results are shown in Fig. 15A indicate that 98 kD MEKK immunoreactivity eluted in fractions 10 to 12. The peak of B-Raf immunoreactivity eluted in fraction 14, whereas Raf-1 was not detected in the eulates from the column. Portions (30 μl) of each fraction from the PC12 lysates of unstimulated control cells or EGF-treated cells were assayed as described above in buffer containing purified recombinant MEK-1 (150 ng) as a substrate. The results shown in Fig. 15B indicate that the peak of MEKK activity eluted in fractions 10 to 12 from EGF-stimulated PC12 cells phosphorylated MEK, whereas little MEK phosphorylation occurred in fractions from unstimulated cells. Example 11 This Example describes studies demonstrating that the phosphorylation of both MEK-1 and the MEKK NH 2 -terminal fusion protein were due to the activity of the 98 kD PC12 cell MEKK. Cell lysates prepared from EGF-stimulated and unstimulated cells were fractionated by FPLC on a Mono-Q column to partially purify the endogenous MEKK. Lysates from unstimulated control PC12 cells or cells treated with EGF (30ng/ml) for 5 minutes were fractionated by FPLC on a Mono Q column,,using a linear gradient of 0 to 525 mM NaCl. A portion (30μl) of each even numbered fraction was mixed with buffer (20mM piperazine-N,N'-bis-2-ethanesulfonic acid (Pipes) (pH 7.0), lOmM MnCl 2 , aprotinin (20μg/ml) , 50mM β- glycerophosphate (pH 7.2), ImM EGTA, IP-20 (50μg/ml) , 50mM NaF, and 30μCi (γ- 32 P)ATP) containing purified recombinant MEK-1 (150ng) as a substrate in a final volume of 40μl and incubated at 30°C for 25 minutes. Reactions were stopped by the addition of 2X SDS sample buffer (40μl) , boiled and subjected to SDS-PAGE and autoradiography. The peak of MEKK activity eluted in fractions 10-12. Portions (30μl) of each even numbered fraction from lysates of EGF-treated PC12 cells were mixed with buffer as described above except containing purified recombinant MEKK NH 2 -terminal fusion protein (400ng) as a substrate instead of MEK-1. Purified recombinant kinase inactive MEK-1 or the MEKK NH 2 -terminal fusion protein were then used as substrates in the presence of (γ- 3 P)ATP to determine whether 98 kD MEKK directly phosphorylates either substrate. Fractions 10-14 of lysate from PC12 cells treated with EGF phosphorylated MEK-1 while little MEK-1 phosphorylation occurred in untreated control fractions. The MEKK NH 2 -terminal fusion protein was also phosphorylated in the same fractions as was MEK-1, although the peak of activity was slightly broader (fractions 8-16) . Referring to Fig. 16, immunoblotting of column fractions demonstrated that the 98 kD MEKK protein co- eluted with the peak of activity that phosphorylated either exogenously added kinase inactive MEK-1 or the 50 kD MEKK NH 2 -terminal fusion protein. Portions (900μl) of even numbered column fractions were concentrated by precipitation with trichloroacetic acid and immunoblotted with MEKK antibody. The peak of immunoreactivity eluted in fractions 10-12. Example 12 This Example describes the activation of MEK by a 98 kD MEKK. 98 kD MEKK was immunoprecipitated using the MEKK,_ 369 antiserum described in Example 1 from untreated (-) or EGF- treated (+) PC12 cell lysates. The immunoprecipitates were incubated in the presence (+) or absence (-) of purified recombinant wild-type MEK (150 ng) and in the presence of purified recombinant catalytically inactive MAPK (300 ng) and (γ- 32 P)ATP. The results shown in Fig. 17A indicate that immunoprecipitated MEKK from EGF-stimulated cells phosphorylated and activated MEK, leading to MAPK phosphorylation. No phosphorylation of MAPK occurred in the absence of added recombinant MEK. Immunoblotting demonstrated that there was no contaminating MAPK (Fig. 17B) or contaminating MEK (Fig. 17C) in the MEKK immunoprecipitates from the EGF-stimulated PC12 cells. Thus, phosphorylation and activation of MEK is due to EGF stimulation of MEKK activity measured in the immunoprecipitates. Example 13 This Example describes whether 98 kD PC12 cell MEKK and Raf-B require functional Ras proteins for growth factor mediated signalling. Dominant negative Ha-ras(Asn 17) (N 17 Ras) was expressed in PC12 cells and EGF-stimulated MEKK or Raf-B activation was assayed in immunoprecipitates using kinase inactive MEK-1 as a substrate. PC12 cells stably expressing dexamethasone inducible N 17 Ras were serum starved for 18-20 hours in media containing 0.1% BSA with or without lμM dexamethasone and then untreated or treated with EGF (30ng/ml) for 5 minutes. Equal amounts of soluble protein from cell lysates was immunoprecipitated with either MEKK or Raf-B antisera and incubated with purified recombinant catalytically inactive MEK-1 and (γ- 32 P)ATP as described above. Expression of N 17 Ras was induced in PC12 clones stabley transfected with the N 17 Ras gene by the addition of dexamethasone to the starvation media. N 17 Ras expression inhibited the activation of MEKK by EGF as measured by its ability to phosphorylate kinase inactive MEK. EGF-mediated activation of Raf-B was also greatly reduced in N 17 Ras expressing PC12 cells compared to uninduced N 17 Ras transfectants. Addition of dexamethasone to wild type PC12 cells had no effect on the magnitude of MEKK or Raf-B activation elicited by EGF. PC12 cell clones stably transfected with the N 17 Ras gene are less responsive to EGF- mediated activation of MEKK activity than are wild type PC12 cells. These results indicate that functional Ras is required for growth factor stimulated activation of both Raf-B and MEKK in PC12 cells, suggesting that Ras may mediate its effects on cell growth and differentiation through the activation of multiple protein kinase effectors from both the Raf and MEKK families. Thus, EGF stimulated a peak of MEKK activity within 5 minutes which persisted for at least 30 minutes following treatment, and was similar to the timecourse of Raf-B activation. Nerve growth factor (NGF) and the phorbol ester TPA also activated MEKK, although to a lesser degree than EGF. MEKK activity in immunoprecipitates or column fractions was dissociable from that of EGF-stimulated c-Raf-1 and Raf-B activities. Forskolin pretreatment abolished both MEKK and Raf-B activation by EGF, NGF, and TPA (Fig. 18) . Both MEKK and Raf-B activation in response to EGF was inhibited by stable expression of dominant negative N 17 Ras. These findings represent the first demonstration of Ras-dependent MEKK regulation by growth factors and suggest the emergence of a complex intracellular kinase network in which Ras may alternately couple between members of the Raf and MEKK families. To determine whether the growth factor-mediated activation of 98 kD PC12 cell MEKK was inhibited by PKA, forskolin was used to elevate intracellular cAMP and activate PKA. Serum-starved PC12 cells were pretreated with or without forskolin (50μM) for 3 minutes to activate protein kinase A and then with EGF (30ng/ml) , NGF (lOOng/ml) , or TPA (200nM) for 5 minutes and MEKK was immunoprecipitated from equal amounts of soluble protein from cell lysates and incubated with purified recombinant catalytically inactive MEK-1 and (γ- 32 P)ATP as described above. Raf-B activity was also assayed from the same cell lysates to test whether its regulation differed from that of MEKK. Raf-B was immunoprecipitated from the same cell lysates as described above and assayed for its ability to phosphorylate MEK-1 as described above. Forskolin pretreatment abolished the activation of both MEKK and Raf- B by EGF, NGF, and TPA, as measured by their ability to phosphorylate kinase-inactive MEK-1 (Fig. 18) . Forskolin treatment alone had no appreciable effect on either kinase. These results demonstrate that in addition to Raf-1 and Raf-B, PKA activation inhibits growth factor stimulation of 98 kD PC12 cell MEKK, suggesting the existence of a common regulatory control point for PKA action which lies between or downstream of Ras and upstream or at the level of each of these three kinases. Example 14 This Example describes the determination of whether a similar or distinct MEK activity is involved in activation of MAPK though G. protein coupled receptors by measuring MEK activity in cell lysates from thrombin stimulated Rat la cells. Thrombin stimulated cells exhibited a MEK activity which co-fractionated with the major MEK peak detected in EGF stimulated cells. The magnitude of MEK activity from thrombin challenged cells was generally two to three-fold less than that observed with EGF stimulation, which correlates with the smaller MAPK response the present inventors have observed in thrombin challenged cells. Differential regulation of MEK in Rat la and NIH3T3 cells expressing gip2 , v-src, v-ras , or v-raf led the present inventor to investigate the protein kinases that are putative regulators of MEK-1. Recently, it was shown that Raf-1 can phosphorylate and activate MEK. Raf activation was assayed in the following manner. Cells were serum starved and challenged in the presence or absence of the appropriate growth factors, as described above. Serum starved Rat la cells were challenged with buffer alone or with EGF and Raf was immunoprecipitated using an antibody recognizing the C terminus of Raf. Cells were lysed by scraping in ice cold RIPA buffer (50 mM Tris, pH 7.2, 150 mM NaCl, 0.1% SDS, 0.5% sodium deoxycholate, 1.0% Triton X 100, 10 mM sodium pyrophosphate, 25 mM sodium glycerophosphate, 2mM sodium vanadate, 2.1 μg/ml aprotinin) and were microfuged for 10 min to remove nuclei. The supernatants were normalized for protein content and precleared with protein A Sepharose prior to immunoprecipitation with rabbit antiserum to the C terminus of Raf-1 and protein A Sepharose for 2-3 h at 4°C. The beads were washed twice with ice cold RIPA and twice with PAN (10 mM Pipes, pH 7.0, lOOmM NaCl, 21μg/ml aprotinin). A portion of the immunoprecipitate was diluted with SDS sample buffer and used for immunoblot analysis. The remainder was resuspended in kinase buffer (20 mM Pipes pH 7.0, 10 mM MnCl 2 , 150 ng kinase-inactive MEK-1, 30 μCi γ- 32 P- ATP and 20 μg/ml aprotinin) in a final volume of 50 μl for 30 min at 30°C. Wild type recombinant MEK-1 was autophosphorylated in parallel as a marker. Reactions were terminated by the addition of 12.5 μl 5X SDS sample buffer, boiled for 5 minutes and subjected to SDS-PAGE and autoradiography. The immunoprecipitated Raf, in the presence of γ- 3 P- ATP, was able to phosphorylate MEK-1. The recombinant MEK- 1 used in this assay was kinase inactive to ensure it did not autophosphorylate as is observed with wild type MEK-1. Little or no phosphorylation of MEK-1 by Raf was observed in immunoprecipitates from control cells. EGF challenge clearly stimulated Raf catalyzed phosphorylation of MEK-1; in contrast, thrombin challenge of Rat la cells did not measurably activate Raf even though endogenous MEK was clearly activated. EGF stimulated Raf phosphorylation of recombinant MEK-1 by approximately 2.6-fold over basal. Little phosphorylation of MEK by Raf was observed in Raf immunoprecipitates from Gip2 or v-Src expressing Rat la cells. EGF stimulation was still capable of activating Raf catalyzed phosphorylation of MEK-1 in these cell lines by 1.8 and 1.4-fold, respectively. The blunting of the EFG response in Gip2 and v-Src expressing cells is likely a result of desensitization of the EFG receptor upon constitutive activation of MAPK. The amount of Raf in the immunoprecipitates was shown to be similar by subsequent SDS-PAGE and immunoblotting using Raf antibody. Since thrombin stimulation of MEK is two to three-fold over basal, at least a 1.5-fold stimulation of MEK phosphorylation is expected if Raf significantly contributed to MEK activation by this growth factor. This level of activation was detectable in the EGF stimulated Gip2 and v-Src expressing cells lines. Thus, it is unlikely that the failure to detect thrombin activation of Raf is due to the sensitivity of the assay. Thrombin stimulation of MAPK is maximal at 3 minutes. Stimulation of Rat la cells for 1 or 5 minutes with thrombin did not increase Raf activity. In NIH3T3 cells, as in Rat la cells, EGF activates Raf approximately 2.7-fold, while thrombin does not. V-Raf expressing NIH3T3 cells showed no increase in MEK-1 phosphorylation. This result was unexpected since MEK was clearly activated in v-Raf expressing NIH3T3 cells. Both the p90 and p75 gag-raf fusion proteins in addition to c- Raf-1 were immunoprecipitated from v-Raf NIH3T3 cells by the antisera. P75gag-raf has been shown to exhibit protein kinase activity, but it is possible that the NH 2 terminal gag fusion protein sterically hinders Raf phosphorylation of recombinant MEK-1 in the in vitro assay system. Further studies will have to be done to measure v-Raf kinase activity. The results argue that activation of MEK cannot be accounted for exclusively by the activation of Raf. Additional regulatory kinases for MEK must exist which contribute to MEK activation in thrombin stimulated, G. protein coupled pathways and in gip2 and v-src transfected cells. Example 15 This Example demonstrates the ability of a PPPSS-trunc and Ncol-trunc of MEKK protein to activate MAPK activity compared with full-length MEKK protein and a negative control protein. The results shown in Fig. 19 indicate that the truncated MEKK molecules were more active than the full- length MEKK. Indeed, the truncated MEKK molecules were at least about 1.5 times more active than full-length MEKK protein. Thus, removal of the regulatory domain of MEKK deregulates the activity of the catalytic domain resulting in improved enzyme activity. Example 16 This example describes the preferential activation of JNK by MEKK compared with Raf. HeLa cells were transiently transfected with truncated MEKK 370 _ 738 under control of an inducible mammary tumor virus promoter, together with epitope tagged JNKl (described in detail in Derijard et al., p. 1028, 1994, Cell , Vol. 76). Other HeLa cells were also transiently transfected with truncated BXB-Raf under control of an inducible mammary tumor virus promoter, together with epitope tagged JNKl (Derijard et al., ibid. ) . The following day, MEKK^.-^ g expression and BXB-Raf expression were induced by administration of dexamethasone (10 μM) for 17 hours. Cell extracts were then prepared and assayed for JNK activity using an immune complex kinase assay (detailed in Derijard et al., ibid. ) . Phosphorylation was quantitated by phosphorimager analysis. The results shown in Fig. 20 indicate that MEKK stimulated about 30-fold to about 50- fold activation more JNK activity over unstimulated cells (basal) and about 15-fold to about 25-fold JNK activity over Raf stimulated cells. Example 17 This example describes that the phosphorylation of c- Myc transactivation domain in response to MEKK expression activates MYC-GAL 4 transcriptional activity. Two separate expression plasmids were constructed as follows. The expression plasmid pLNCX was ligated to a cDNA clone comprising c-myc (1-103) ligated to GAL4 (1-147) (Seth et al., pp. 23521-23524, 1993, J. Biol . Chem . , Vol. 266) to form the recombinant molecule pMYC-GAL 4. The expression plasmid UAS G -TK Luciferase (Sadowski et al., pp. 563-564, 1988, Nature , Vol. 335) was transfected with either pMYC-GAL 4 or pLU-GAL into Swiss 3T3 cells using standard methods in the art to form recombinant cells herein referred to as LU/GAL cells. Recombinant control cells were also produced by transfecting in pGAL4-Control plasmids containing GAL4 (1-147) alone in the absence of c- myc (1-103). LU/Gal cells were transfected with either pMEKK 370 . 738 , pMEKK (encoding full-length MEKK^ g ) , BXB-Raf, pMyc-Gal4, pCREB-Gal4 (encoding CREB_,. 261 fused to Gal 4 1 _ 147 ; Hoeffler et al., pp. 868-880, 1989, Mol . Endocrinol . , Vol. 3), pGal4, or CREB fusion protein referred to as GAL4. The transfected cells were incubated overnight and then lysed using methods standard in the art. The luciferase activity of each cell lysate was measure on a luminometer. The results shown in Fig. 21 indicate that MEKK is selectively capable of stimulating the phosphorylation of c-Myc transactivation domain in such a manner that the c-Myc domain is activated and induces transcription of the transfected luciferase gene. In addition, the results indicate that MEKK does not stimulate CREB activation. Also, activated Raf is unable to stimulate Myc activation. A schematic representation of the activation mechanism of c-Myc protein by MEKK is shown in Fig. 23. Example 18 This Example describes the phosphorylation of p38 MAPK protein by MEKK 3 protein and not MEKK 1 protein. COS cells were transfected with the expression plasmid pCVM5 ligated to cDNA clones encoding either MEKK 1 or MEKK 3 protein, or a control pCVM5 plasmid lacking MEKK cDNA inserts. Forty-eight hours after transfection, the COS cells were lysed and the lysate fractionated on a Mono Q FPLC column using conditions described in Example 4. The fractions were analyzed for tyrosine phosphorylation of MAP kinase-like enzymes using the kinase assay described in Example 4. Referring to Fig. 23, expression of MEKK 3 induces tyrosine phosphorylation of p38 MAPK and the p42 and p44 forms of MAPK. MEKK 1, however, only induces weak phosphorylation of p38 MAPK but does induce phosphorylation Of p42 and p44 MAPK. Example 19 This example describes MEKK-induced apoptosis. Cells were prepared for the apoptosis studies as follows. Swiss 3T3 cells and REF52 cells were transfected with an expression plasmid encoding β-Galactoctosidase (β- Gal) detection of injected cells. One set of β-Gal transfected cells were then microinjected with an expression vector encoding MEKK^.^ g protein. Another set of β-Gal transfected cells were then microinjected with an expression vector encoding truncated BXB-Raf protein. A. Beauvericin-induced apoptosis A first group of transfected Swiss 3T3 cells and REF52 cells were treated with 50 μM beauvericin for 6 hours at 37°C. Beauvericin is a compound known to induce apoptosis in mammalian cells. A second group of cells were treated with a control buffer lacking beauvericin. The treated cells were then fixed in paraformaldehyde and permeabilized with saponin using protocols standard in the art. The permeabilized cells were then labelled by incubating the cells with a fluorescein-labelled anti-tubulin antibody (1:500; obtained from GIBCO, Gaithersburg, MD) to detect cytoplasmic shrinkage or 10 μM propidium iodide (obtained from Sigma, St. Louis, MO) to stain DNA to detect nuclear condensation. The labelled cells were then viewed by differential fluorescent imaging using a Nikon Diaphot fluorescent microscope. Fig. 24 shows two fields of Swiss 3T3 cells and REF52 cells, one field representing cells treated with the control buffer and a second field representing cells treated with beauvericin. The cells treated with beauvericin demonstrated cytoplasmic shrinkage (monitored by the anti-tubulin antibodies) and nuclear condensation (monitored by the propidium iodide) characteristic of apoptosis. B. MEKK-induced apoptosis Swiss 3T3 cells and REF52 cells microinjected with a β-galatoctosidase expression plasmid, and an MEKK encoding plasmid or a BXBrRaf encoding plasmid, were treated and viewed using the method described above in Section A. An anti-β-Gal antibody (1:500, obtained from GIBCO, Gaithersburg MD) was used to detect injected cells. Referring to Fig. 25, microscopic analysis of REF52 cells indicated that the cells expressing MEKK protein underwent cytoplasmic shrinkage and nuclear condensation leading to apoptotic death. In contrast, cells expressing BXB-Raf protein displayed normal morphology and did not undergo apoptosis. Similarly, referring to Fig. 26, microscopic analysis of Swiss 3T3 cells indicated that the cells expressing MEKK protein underwent cytoplasmic shrinkage and nuclear condensation leading to apoptotic death. In contrast, cells expressing BXB-Raf protein displayed normal morphology and did not undergo apoptosis. Fig. 27 shows 3 representative fields of RFE52 cells expressing MEKK protein which have undergone substantial cytoplasmic shrinkage and nuclear condensation compared with a control cell not expressing MEKK. Similarly, Fig. 28 shows 3 representative fields of Swiss 3T3 cells expressing MEKK protein which have undergone substantial cytoplasmic shrinkage and nuclear condensation compared with a control cell not expressing MEKK. Thus, MEKK and not Raf protein can induce apoptotic programmed cell death. Example 20 This Example describes regulation of MAPK activity by both MEKK and Raf protein. COS cells were prepared using the method described in Example 3. In addition, COS cells were transfected with the pCVMV5 Raf construct (1 μg: Raf) . FPLC MONO Q ion- exchange column fractions were prepared as described in Example 3 and assayed for MAPK activity according to the method described in Heasley et al., ibid. Referring to Fig. 29, both MEKK and Raf overexpression in COS 1 cells resulted in similar levels of stimulation of MAPK activity over basal levels. The foregoing description of the invention has been presented for purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge in the relevant art are within the scope of the present invention. The preferred embodiment described herein above is further intended to explain the best mode known of practicing the invention and to enable others skilled in the art to utilize the invention in various embodiments and with various modifications required by their particular applications or uses of the invention. It is intended that the appended claims be construed to include alternate embodiments to the extent permitted by the prior art.

Claims: What is Claimed: 1. An isolated protein comprising at least a portion of an amino acid sequence encoded by a nucleic acid sequence that is capable of hybridizing under stringent conditions with a nucleic acid molecule encoding an amino acid sequence selected from the group consisting of SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10. 2. A formulation comprising at least one isolated protein having at least a portion of an amino acid sequence encoded by a nucleic acid sequence that is capable of hybridizing under stringent conditions with a nucleic acid molecule encoding an amino acid sequence selected from the group consisting of SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8 and SEQ ID NO:10. 3. An isolated nucleic acid molecule capable of hybridizing under stringent conditions with a nucleic acid sequence selected from the group consisting of SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and SEQ ID NO:9. 4. A recombinant molecule, comprising a nucleic acid molecule capable of hybridizing under stringent conditions with a nucleic acid sequence selected from the group consisting of SEQ ID NO:l, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7 and SEQ ID NO:9, said nucleic acid molecule being operatively linked to an expression vector. 5. A recombinant cell transformed with a recombinant molecule, comprising a nucleic acid molecule operatively linked to an expression vector, said nucleic acid molecule comprising a nucleic acid sequence capable of hybridizing under stringent conditions with a nucleic acid sequence selected from the group consisting of SEQ ID N0:1, SEQ ID N0:3, SEQ ID N0:5, SEQ ID N0:7 and SEQ ID N0:9. 6. A method for regulating the homeostasis of a cell comprising regulating the activity of an MEKK-dependent pathway relative to the activity of a Raf-dependent pathway in said cell. 7. A method to treat a medical disorder, comprising regulating the activity of an MEKK-dependent pathway relative to the activity of a Raf-dependent pathway in a cell. 8. A method to inhibit a medical disorder selected from the group consisting of tumorigenesis and autoimmunity, comprising regulating the activity of an MEKK-dependent pathway relative to the activity of a Raf- dependent pathway in a cell to inhibit the growth of said cell. 9. A therapeutic compound capable of regulating the activity of an MEKK-dependent pathway in a cell identified by a process, comprising: a) contacting a cell with a putative regulatory molecule; and b) determining the ability of said putative regulatory compound to regulate the activity of an MEKK- dependent pathway in said cell by measuring the activation of at least one member of said MEKK-dependent pathway. 10. A method to treat a disease, comprising administering to a patient an effective amount of a therapeutic compound comprising at least one regulatory molecule selected from the group consisting of a molecule capable of decreasing the activity of a Raf-dependent pathway, a molecule capable of increasing the activity of an MEKK-dependent pathway, and combinations thereof, wherein said effective amount comprises an amount which results in the depletion of harmful cells involved in said disease.

Inventors: JOHNSON GARY L, JOHNSON, GARY, L.
Applicants: JOHNSON GARY L, NAT JEWISH CT IMMUN & RESPIRAT, JOHNSON, GARY, L., NATIONAL JEWISH CENTER FOR IMMUNOLOGY AND RESPIRAT
Application year: 1994
Main classification: C07K14
IPC codes: A61K38, C12N9